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Gas-Engine Details 


» 

V' D 

By 

I.C.S. STAFF 


GAS-ENGINE DETAILS 
GAS-ENGINE LUBRICATION 
CARBURETERS 


356 

Published by 

INTERNATIONAL TEXTBOOK COMPANY 


SCRANTON, PA. 



r j mo 

‘16 


Gas-Engine Details: Copyright, 1919, 1907, by International Textbook Com¬ 
pany. 

Gas-Engine Lubrication: Copyright, 1920, 1907, by International Textbook 

Company. 

Carbureters: Copyright, 1920, 1916, 1907, by International Textbook Company. 


Copyright in Great Britain 


All rights reserved 


Printed in U. S. A. 




International Textbook Press 


Scranton, Pa. 


71463 





CONTENTS 


Note. —This book is made up of separate parts, or sections, as indicated by 
their titles, and the page numbers of each usually begin with 1. In this list of 
contents the titles of the parts are given in the order in which they appear in 
the book, and under each title is a full synopsis of the subjects treated. 


GAS-ENGINE DETAILS 

Pages 


Parts of Gas Engines. 1-32 

Frames . 1-2 

Cylinders. 3-11 

Cylinder, head, and jacket in one piece; Cylinder with sepa¬ 
rate head; Cylinders of automobile engines; Cylinders 
for large double-acting engine; Water-jackets; Air¬ 
cooled cylinders. 

Pistons. 12-15 

Trunk type of piston; Piston for double-acting engine; 

Piston rings. 

Crossheads. 16 

Connecting-Rods . 16-18 

Crankshafts . 19-20 

Flywheels. 21-22 

Valves . 23-26 

Valve Mechanism . 27-29 

Miscellaneous Engine Fittings. 30-32 













IV 


CONTENTS 


GAS-ENGINE LUBRICATION 

Pages 

Purpose and Nature of Lubricants. 1-26 

Friction and Lubrication. 1 

Lubricants .. 2- 8 

Oils; Cylinder oil; Grade of oil; Greases; Automobile 
greases. 

Lubricating Systems and Devices. 9-17 

Lubricating film; Gravity system; Forced-feed system; 
Combination systems. 

Automobile-Engine Lubrication . 18-26 

Classification; Splash lubrication system; High-pressure 
lubrication systems; Cylinder lubricators; Pump lubri¬ 
cator. 

Bearings.. 27-59 

Shaft Bearings . 27-44 

General considerations; Oil grooves in bearings; Types 
of bearings; Plain bearings; Roller bearings; Ball 
bearings; Taking up wear in bearings. 

Hot Bearings . 44—59 

Observation of bearings; General treatment of hot bear¬ 
ings; Causes and prevention of hot bearings. 










CONTENTS 


v 


CARBURETERS 

Pages 

Formation of Explosive Mixtures. 1-57 

Effects of Changes in Proportions. 1-4 

Devices for Making Explosive Mixtures. 5-51 

Carbureters for Stationary Engines. 5-23 

Carbureters for Automobile and Aeroplane Engines... 24-43 

Carbureters for Tractors. 44-51 

Fuel Supply . 52-57 

Gravity-feed system; Pressure-feed system; Vacuum-feed 
system. 











GAS-ENGINE DETAILS 


Serial 1859 - Edition 1 

PARTS OF GAS ENGINES 


FEATURES OF CONSTRUCTION 


FRAMES 

1. Requirements of the Frame. —The main structure 
of an engine, on which the various other parts are mounted, is 
called the frame or base. It must be rigid and substantial so 
as to withstand the shocks resulting from successive explosions 
in the cylinder, and from vibration due to the reciprocating and 
rotating parts. The frame should be so constructed that the 
working parts of the engine can easily be reached for inspec¬ 
tion, cleaning, and repairs. 

2. Standard Types of Frames.— The principles 
involved in the design of gas-engine frames have standardized 
the construction to a large extent, the type depending somewhat 
on the size of the engine. A common type of frame for engines 
of small and medium powers is shown in Fig. 1. The sides a of 
the frame are low, as shown, thus giving easy access to the 
interior of the cylinder and the reciprocating parts. The over¬ 
hung cylinder required with this frame is attached by means of 
the stud bolts b. The main bearing c is divided at an angle, 
usually 45°, so that the wear due to the weight and the thrust 
from the explosions in the cylinder comes on the face of the 
bearing instead of on the joint. 


COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ALL RIGHTS RESERVED 





2 


GAS-ENGINE DETAILS 


3. In the larger types of engines, especially where very 
steady running is required, the frame is frequently constructed 

as shown in Fig. 2. 
In this design the 
sides a form a straight 
and rigid connection 
between the cylinder 
and the main bear¬ 
ings b. The cylinder 
^ shell, or jacket, c and 
the frame are cast in 
one piece so that the 
parts cannot get out of alinement. The cylinder is supported 
throughout its length by the frame and consequently the 
vibration, sometimes experienced with large engines with 
overhung cylinders, is avoided. 

4. A section through the frame of a vertical stationary 
engine is shown in Fig. 3. The frame is made up of two parts, 
the upper base a and the lower base b, and forms a crank-case 
of the enclosed type in which surplus oil from the bearings is 
collected. The dotted outline c shows the position of the cylin¬ 
der when mounted in place on the frame. The main bearings d, 




which carry the crank-shaft, are mounted in the .ower base and 
are adjusted vertically by means of wedges e, which may be 










GAS-ENGINE DETAILS 


3 


moved horizontally by turning the threaded rods /. The upper 
base is connected to the lower base by bolts g and heavy rods h 
which take the stress due to the explosions. Openings i are 
provided on both sides of 
the crank-case opposite each 
crank to permit the inspec¬ 
tion and adjustment of the 
working parts. The frame 
is strengthened and stiffened 
by webs j cast at intervals. 


CYLINDERS 

5. Cylinder, Head, 
and Jacket in One Piece. 

A sectional view of a cylin¬ 
der of a vertical, four-cylin¬ 
der, tractor engine of the 
four-cycle type, having the 
cylinder a, head b, and 
water-jacket c cast in one 
piece, is shown in Fig. 4. 

The object of this construc¬ 
tion is to avoid packing joints between the cylinder and head 
and between the cylinder and water-jacket. One-piece cylinder 
castings can be made very satisfactorily for small or medium¬ 
sized engines but it is not usually considered good practice to 
use such castings for engines of large size. 

6. Cylinders of horizontal stationary engines of the four¬ 
cycle type are usually cast with water passages cored in the 
sides and head, as shown in Fig. 5. A cover a carrying the 
igniter plug b is bolted to the head, and a cover ring c is bolted 
to the crank end of the water-jacket. The inlet valve is located 
at d and the exhaust valve at e. The ring c provides a conve¬ 
nient means of cleaning the water-jacket of any dirt or sedi¬ 
ment that may accumulate from the use of dirty or impure 
water. Since the water pressure in the water-jacket is small, 
ordinary packing is used to keep the joint tight. 























4 


GAS-ENGINE DETAILS 


An outside view of this cylinder is shown in Fig. 6. The 
opening a is for the igniter; that on top, at d, is for the inlet 
valve, and a corresponding one at e, at the bottom, is for the 
exhaust valve. The gas-inlet pipe is connected to the opening 
shown at / and the exhaust pipe at g ; chambers are cored from 
these openings to the valves. At h is an oil hole, and at i is the 
outlet for the cooling water as it leaves the water-jacket. On 
each side of the cylinder there is a bracket like the one shown 

at j, by means of which the 
cylinder is bolted to the 
frame or engine bed. 

7. There are disad¬ 
vantages as well as advan¬ 
tages in having the cyl¬ 
inder, head, and water- 
jacket cast in one piece. 
Some of the disadvantages 
of this construction are the 
difficulty or impossibility 
of determining the thick¬ 
ness of metal in the cylin¬ 
der walls or water-jacket 
and the difficulty of in¬ 
specting the closed end of 
the cylinder when machin¬ 
ing, or when it is suspected 
that there is an accumula¬ 
tion of carbon in the com¬ 
bustion chamber. Casting the head and cylinder in one piece 
also makes it difficult to counterbore the cylinder and secure a 
good finished surface. A section a of a part of the piston is 
shown in Fig. 7 ; at b, a sectional view of part of the cylinder is 
given, showing the counterbore c, or the portion of the cylinder 
bored to a slightly greater diameter than that in which the pis¬ 
ton fits, so that, as the surface of the cylinder wears away, it 
will not leave a shoulder or raised ring for the piston to strike. 
Experience has shown, however, that counterboring a gas- 



Fig. 4 











































GAS-ENGINE DETAILS 


5 


engine cylinder is sometimes likely to do more harm than good, 
especially if the counterbore extends, as it usually does, to the 


ale 



middle of the outer piston ring, as shown at d. In such a case, 
the outer ring may do very little toward preventing the gas 
from leaking around the piston. 

8. Cylinder With Separate Head —When the cylinder 
is provided with a separate removable water-jacketed head, 
as shown in Fig. 8, the head end of the cylinder and the water- 
jacketed head contain passages, as shown at a, through which 



the cooling water circulates. The shape of these openings in the 
cylinder is shown more clearly in the enlarged view of the top 










































































6 


GAS-ENGINE DETAILS 


of the cylinder with the head removed in Fig. 9, the water 
passages being shown at a . The openings in the head and in 



the head end of the cylinder must match when they are put 
together, and any gasket placed between them must have holes 




















































GAS-ENGINE DETAILS 


7 


cut to match these openings. The bolt holes must be so located 
that the joint may be made tight. Occasionally, the openings 
are made round, so that a 
part or all of them may 
readily be tapped and 
plugged. Since these pas¬ 
sages should be as large as 
possible, the thickness of the 
metal on the inside forming 
the cylinder wall and that on 
the outside is sometimes 
made as little, in the case of 
small engines, as J or J inch. 

The strips, shown at b, are 
so narrow that it is only with 
difficulty that the joint is 
made tight at these points under the high pressures developed 
in the gas-engine cylinder. Cylinder heads for small engines 
are sometimes made so thin that they will spring between the 
studs shown at c, allowing the gasket, or packing, to be blown 
out by the pressure; this is due to faulty design. 

9. The head and cylinder are sometimes put together with 
a ground joint—that is, no packing or gasket is used between 
them—but such a joint is difficult to keep in good condition 
where the head must be removed for inspection or repairs. 
The difficulty of bringing the surfaces to such a condition that 




they will not leak is so great that very often a gasket must be 
used after the head has been removed a few times. Some 

























8 


GAS-ENGINE DETAILS 


manufacturers omit the cored openings for communication 
between the water-jacket and the head, using an outside con¬ 
nection instead, either cast on as shown in Fig. 10 ( a ) or con¬ 
nected by means of pipe connections as shown in (b). In (a), 
the water passage a is cored in the lugs b in the cylinder and 

head. In ( b ), the 
connection is made 
by means of two short 
nipples a, a union el¬ 
bow b, and a common 
elbow c. 



10. Cyli nders 
of Automobile 
Engines. — The 
form of an automo¬ 
bile - engine cylinder 
depends on the loca¬ 
tion and arrangement 
of the inlet and ex¬ 
haust valves. The 
cylinders are some¬ 
times made as shown 
in Fig. 11, in which 
case they are known 
as the T -head type. 
The inlet valve a and 
the exhaust valve b 
are located on opposite 
sides of the cylinder, 
giving it, roughly, the 
appearance of the let¬ 
ter T. In the cylinder head is the priming cock c, used for 
admitting gasoline when starting the engine. The screwed 
plugs d over the inlet and exhaust valves make them accessible 
for repairs. Sometimes the inlet and exhaust valves are placed 
together on the same side of the cylinder and are operated by 
the same cam-shaft. The cylinders are then said to be of the 


Fig. 11 








































GAS-ENGINE DETAILS 


9 


L -head type. A construction is sometimes used in which the 
inlet and exhaust valves are placed in the cylinder head, the 
valves being operated by push rods and rocker-arms. This 
is known as the I -head, or valve-in-head, type. 

H* Cylinder for Large Double-Acting Engine. 
Gas engines for power-plant work aie often built in large 
sizes. Many of these large engines are double-acting; that is, 
work is done on both sides of the piston. The cylinder of a 
double-acting engine is somewhat different from the cylinder 



of a single-acting engine, in which work is done on one side of 
the piston only. The cylinder for a large double-acting engine 
is shown in section in Fig. 12. The cylinder barrel a, in which 
the piston works, is surrounded by a water-jacket that is cast 
split; that is, a part of the jacket wall at the center is omitted 
and the opening is then closed by means of a band b drawn 
tight by bolts. This construction is sometimes used on large 
gas-engine cylinders as it simplifies the casting, prevents exces¬ 
sive casting stresses, and, under working conditions, relieves 
temperature stresses resulting from unequal expansion in the 























































































































10 


GAS-ENGINE DETAILS 


jacket wall and the cylinder barrel. The ends of the cylinder 
are closed by water-cooled heads c, one of which is shown in 
section. The leakage of gas around the piston rod is pre¬ 
vented by the use of metallic packing, shown at d. The inlet- 
valve cages e are located at the top of the cylinder and the 
exhaust-valve cages / are placed at the bottom, as shown. 

12. Water-Jackets. —In order to prevent the high tem¬ 
perature inside the cylinder from overheating and damaging 
the piston and cylinder, it is necessary to keep them cool by cir¬ 
culating water around the cylinder, or by some equivalent 
means. Hence, the water-jacket that surrounds the cylinder is 
one of the important features of the internal-combustion 
engine. From a scientific point of view, a stream of water 
circulating around a cylinder in which a flame is burning is very 
wasteful, but for general use nothing better has yet been found. 
For small engines, however, it is found possible under certain 
conditions to substitute a strong current of air that strikes 
directly on the outer surface of the cylinder. 

13. Great care must be taken to select lubricating oils that 
will stand as high temperatures as those reached in the cylinder 
walls. Difficulty would be found in employing higher temper¬ 
atures, for the reason that the fresh charges would be likely 
to ignite from contact with the hot cylinder walls. When such 
inflammable fuel as gasoline is used under high compression, it 
is necessary, in order to avoid premature explosion, to keep 
the walls of the combustion chamber, the piston head, and the 
valves reasonably cool. 

14. Air-Cooled Cylinders.— The internal construction 
of an air-cooled cylinder is the same as that of a water-cooled 
cylinder; also, the arrangement of the valves and other 
mechanism is similar. The external surface of an air-cooled 
cylinder, however, is extended, or increased, by various means, 
usually by the use of thin heat-radiating flanges, or ribs, cast 
on the cylinder walls or fitted to them. These ribs, or flanges, 
serve to conduct the heat from the cylinder walls, the heat 
being absorbed and carried away by the air that comes in con¬ 
tact with the flanges. In some of the earlier air-cooled engines, 



GAS-ENGINE DETAILS 


11 


the cylinuers were provided with pins, or studs, radiating from 
the outer surface of the casting. These studs, which were 




Fig. 13 

screwed into the cylinder walls were sometimes threaded from 
end to end in order to provide a greater heat-radiating surface. 

15. A good example of the air-cooled cylinder is shown in 
Fig. 13. The construction is of the valve-in-head type. Two 
cylinders are illustrated, a sectional view of one and an external 
view of the other being shown in (a) and a top view of one of 


356—2 
















































































12 


GAS-ENGINE DETAILS 


these cylinders in ( b ). Like parts are lettered the same in each 
view. A large heat-radiating surface is obtained by the use of 
vertical steel flanges a that are cast on the wall b of the cylin¬ 
der. The flanges are spaced about £ inch apart around the 
entire outer circumference of the cylinder and project radially 
outwards a distance of about 1 inch. The average length of 
these flanges is 8 inches. A cylindrical air jacket c surrounds 
each cylinder and, with the cylinder wall, it forms an air-tight 
passage through which the cooling air is drawn. The air is 
thus brought into close contact with the flanges, which conduct 
the heat from the cylinder walls. The inlet valve d and the 
exhaust valve e are located in the cylinder head as shown and 
are operated by push rods and rocker-arms. The valve seats 
are cast in the cylinder head; that is, no valve cages are used. 


PISTONS 

16. Trunk Type of Piston.— Single-acting gas engines 
are provided with hollow cylindrical pistons closed at one end 
and open at the other to receive one end of the connecting-rod, 
as shown in Fig. 14 (a) and (b). Such pistons are of what is 


(') 

known as the trunk type. This form of construction elimi¬ 
nates the crosshead and guides and thus makes possible a more 
compact engine. In order to make the engine as short as pos¬ 
sible, the piston pin is usually set close to the head, or closed, 







































GAS-ENGINE DETAILS 


13 


end of the piston, leaving just room enough for the piston 
rings beyond the piston pin. Near the head end of the piston 
there are three or more grooves a in which are placed piston 
rings, which serve to make a gas-tight joint between the piston 
and the wall of the cylinder. The smaller grooves b, 
Fig. 14 (a), retain and distribute the lubricating oil to all parts 
of the cylinder wall, and thus aid in keeping the gases from 
blowing past the piston. Some pistons have one or two piston 
rings on the crank end of the piston, as shown in ( b ). 

17. In two-cycle engines, the shape of the top of the piston 
is very important, particularly if the transfer port is located in 
the side of the cylinder. The part of the piston that projects 
upwards, as shown at a, Fig. 15 (a), and that deflects the 
incoming charge so that 
it clears the cylinder of 
the burned gases, is 
called a deflector, or 
baffle. Instead of us¬ 
ing such a projection, 
the piston is in some 
cases so shaped as to 
deflect the charge in the 
same manner; such a 
piston is shown in (&). 

The piston of a two- 
cycle engine is made 
about 25 per cent, 
longer than the stroke, because otherwise the exhaust port 
would not remain completely covered during the compression 
stroke and the gas in the crank-case would escape to the 
atmosphere. In three-port, two-cycle engines, a piston ring is 
placed at the lower end of the piston, as shown, to prevent the 
fresh charge in the crank-case from escaping past the piston 
and out of the inlet port. 

18. The piston must be made appreciably smaller in diam¬ 
eter than the cylinder in which it works on account of the 
expansion of the metal due to the high working temperature. 




Fig. IS 














































14 


GAS-ENGINE DETAILS 


As the back, or closed, end of the piston is in contact with the 
burning fuel and becomes the hottest, it is customary to allow 
for greater expansion at this end. An allowance of .002 inch 
for each inch of cylinder diameter may be made over that por¬ 
tion in which the grooves are turned for the rings. For 
example, an engine having a cylinder 6 inches in diameter 
would have the piston made 6X.002 = .012 inch smaller, or 
6—.012 = 5.988 inches in diameter at the back end. The 
remainder of the piston is of slightly larger diameter and may 
be made .001 inch smaller per inch of diameter than the cylin¬ 
der. Thus, for a 6-inch cylinder the front portion of the piston 

would be 6X.001 = .006 inch 
smaller, or 5.994 inches in diam¬ 
eter. 

19. Piston for Double- 
Acting: Engine. — The con¬ 
struction of the piston for a 
double-acting engine is entirely 
different from that of the trunk 
type used on a single-acting 
engine. A double-acting engine 
always has a piston rod to 
which the piston is attached. The large size in which these 
engines are built makes it necessary to cool the piston and pis¬ 
ton rod by circulating water through them. As this type of 
piston is necessarily heavy, it is customary to prolong the piston 
rod through the rear cylinder head, the prolongation being 
called a tail-rod. 

20. A water-cooled piston for a double-acting engine is 
shown in section in Fig. 16. The hollow piston rod a is slightly 
enlarged to receive the piston b, which is held in place by the 
shoulder c and the nut d. A tube e passes through the hollow 
in the piston rod, forming an annular space / around the out¬ 
side of the tube. The thimble g closes the annular space but 
does not close the inside of the tube. The water passes from 
one end of the piston rod, through the tube, direct to the other 
end of the rod, returning through the annular space and cir- 



Fig. 16 




























GAS-ENGINE DETAILS 


15 


culating through the piston as indicated by the arrows. The 
water is supplied to and taken from the piston rod through 
pipes connected by swinging joints or trombone, or slip, joints. 

21. Piston Rings. —A piston ring is made with an open¬ 
ing or split, and is of such width and thickness that it can be 
sprung open enough to slip over the end of the piston and snap 
into the groove. Such a ring is sometimes called a snap ring. 
It is practically the only type of piston ring used in gas engines, 
as it seems to answer the requirements better than any other 
style. The width of the ring should be uniform; it should be 
free in the groove in the piston and 
should be in contact with the cylinder 
for its entire circumference. In order 
to furnish a sufficient packing action 
to the piston, the rings are usually 
made about 1.03 times the diameter 
of the cylinder in which they are to 
be used. Each ring is then cut through 
and a sufficient length of metal is re¬ 
moved to allow the ring to enter the 
cylinder easily. After piston rings 
have been in use for a long time they 
frequently lose their elasticity. Such 
rings can sometimes be improved by 
removing and hammering them on the 
inside with the round peen of a light hammer, but the most 
satisfactory remedy is to replace them with new rings. Piston 
rings should be made of close-grained gray cast iron of uniform 
quality. 




22. Two forms of piston rings that are commonly used are 
shown in Fig. 17. The one shown in (a) is of uniform cross- 
section, with the ends lapped at the parting as shown at a. 
There should be more spring in the ends of the ring than at 
the back b ; consequently, the ring is frequently made eccentric, 
as shown in ( b ). The diagonal parting shown at a in (b) is 
not likely to cut or scratch the cylinder, as no portion of its 
















16 


GAS-ENGINE DETAILS 


parting line is parallel with the motion of the piston. The 
parting shown at a in view (a) is very effective but is more 
difficult to make than the diagonal parting. 


CROSSHEADS 

23. In the single-acting gas engine the trunk type of piston 
serves as a crosshead, but in the double-acting engine, where 
the piston is attached to a piston rod, a separate crosshead must 

be used. The cross¬ 
head shown in Fig. 
18 represents a type* 
that is often used on 
double - acting gas 
engines. The cross¬ 
head body a is a 
steel casting and is 
threaded to receive 
the piston rod b. 
The crosshead i s 
split and clamped on 
the rod by means of 
through bolts c. 
The crosshead pin d 
is straight and is 
held in the cross¬ 
head by means of heavy clamping bolts e. The crosshead 
shoes / are also steel castings and have a swivel connection to 
the body of the crosshead which always gives a full bearing of 
the shoes on the guides. The shoes are adjusted for wear by 
means of eccentric bolts g, which are securely clamped after 
adjustment. 



Fig. 18 


CONNECTING-RODS 

24. Length of Connecting-Rod.—The length of the 
connecting-rod of a horizontal gas engine working on the four¬ 
cycle principle is usually about 2\ times the length of the 
stroke, or, in other words, about 5 times the length of the crank 



























GAS-ENGINE DETAILS 


17 


radius. Vertical engines and large double-acting engines 
usually have shorter connecting-rods so as to make the engine 
more compact. The longer rod causes less wear of the moving 
parts, because in its various positions it does not make such 
large angles with the center line of the engine. 


25. Connecting-Rods for Single-Acting Engines. 
Many types of connecting-rods are used on gas engines; three 




Fig. 19 

of the more common iorms for single-acting engines are shown 
in Fig. 19. The one shown in (a) is rectangular in cross- 
section. The smaller end a is composed of a box containing 
the brasses b that form the piston-pin bearing, and the adjust¬ 
ing wedge c through which the wear of the brasses is taken up. 
The wedge is adjusted by means of the screw d, which is locked 
by a nut when the proper adjustment has been secured. This 
form of connecting-rod end is known as a box end. The large. 





















































18 


GAS-ENGINE DETAILS 


or crankpin, end, or foot, e is attached to the body of the rod 
by bolts f, which also pass through and hold the brasses g and h. 
The outer ends of the bolts are provided with locknuts to 
prevent the nuts from turning while in service. This form of 
connecting-rod end is known as the marine type. 

26. The connecting-rod shown in Fig. 19 ( b ) is of the 
I-shaped section, the large end a being split at right angles to 
the rod through the center of the bearing and having a brass 
lining b. The two parts of the bearing are held together by the 
bolts c and d, which pass through the cap e. The bolts are pro¬ 
vided with locknuts to prevent the nuts from loosening. The 
smaller end / is made solid, bored out, and a brass bushing 
pressed into place, as shown at g. The connecting-rod shown 
in (c) is of circular cross-section. Both ends are of the marine 



type. A hinged end sometimes used on connecting-rods for 
automobile engines is shown in ( d ). The end a and cap b are 
hinged at c, and a screw d is provided to hold the parts together. 
When the piston end of a connecting-rod is made solid and 
bored out, it is frequently provided with a bronze bushing. In 
some engines, the piston pin and the bushing are made of case- 
hardened steel, and both pin and bushing are ground to fit. 

27. Connecting-Rod for Double-Acting Engine. 

In single-acting engines the connecting-rod always takes the 
force of the explosion in compression, or in the form of a push. 
In double-acting engines, however, the force of the explosion is 
taken alternately in compression and tension. For this reason 
it is usually customary to make the crankpin end of the con¬ 
necting-rod solid as well as the crosshead end. A connecting- 
































GAS-ENGINE DETAILS 


19 


rod of this kind, designed for a double-acting engine, is shown 
in Fig. 20. The crankpin end a is machined from the solid 
steel forging and is fitted with babbitted boxes b which may be 
adjusted for wear by means of the wedge c and the bolts d. 
The crosshead end e is also machined from the solid forging 
and fitted with bronze boxes with wedge take-up as shown. 
The body of the rod is rectangular in cross-section. 


CRANK-SHAFTS 

28. Types of Crank-Shafts.— Crank-shafts for gas 
engines are made of steel; those for automobile engine use are 
made of special alloy steels, to obtain lightness and strength. 
They must be strong enough to resist the twisting and bending 
action to which they are subjected, and the bearing portion 
must withstand the wear due to continuous rotation at high 
speed. The type of crank used on single-cylinder gas engines 
is known as the center crank, and has two arms with a crank- 
pin between them. Such a crank is shown in Fig. 21 (a). The 
bearings a and b of the shaft are close to the crank-arms, and 
the crankpin c connects the arms. The two ends of the shaft 
must be in line with each other, and the crankpin must be 
parallel with the shaft. 

29. The type of crank-shaft generally used for two-cylin¬ 
der four-cycle engines when the cylinders are placed side by 
side is shown in Fig. 21 (b). The shaft rests in bearings 
at a, b, and c and the crankpins d and e are in line with each 
other so that the shaft receives an impulse at every revolution. 
To obtain this result with two-cylinder horizontally opposed 
engines the cranks would be placed 180° apart, or opposite each 
other. This latter arrangement is also adopted for two-cylin¬ 
der, two-cycle engines. 

30. The cranks of three-cylinder engines, which are usually 
of the vertical type, are set at an angle of 120° with each other, 
as shown in Fig. 21 (c). This arrangement gives an even 
turning effect and tends to make a smooth running engine. The 
shaft is supported by four bearings and the weight of the 



20 


GAS-ENGINE DETAILS 


reciprocating parts is usually balanced by counterweights a 
attached to the cranks opposite to the crankpins as shown. 

31. A crank-shaft for a four-cylinder vertical engine is 
shown in Fig. 21 ( d ) in which the shaft receives two impulses 



(a) 




Fig. 21 


during each revolution. The two outer crankpins are in line 
and the two inner crankpins are in line, so that the two pair of 
crankpins are 180° apart. Since there are always two pistons 
on the up stroke while the other two are on the down stroke, 
the reciprocating parts tend to balance each other and no 












































GAS-ENGINE DETAILS 


21 


counterweights are required. The crank-shaft shown is sup¬ 
ported by five bearings, but often the second and fourth bear¬ 
ings are omitted, leaving three bearings to support the shaft, 
and in some cases only two bearings are used. The arrange¬ 
ment of the cranks, however, is the same in any case. 

32. Crank-shafts for six-cylinder engines are supported by 
three, four, or seven bearings. The crank-shaft shown in 
Fig. 21 ( e ) is carried on four bearings. The journals that 
run in the bearings are shown at a and the crankpins at b. The 
cranks are arranged in pairs, one and six forming a pair, two 
and five forming a pair, and three and four forming a pair. 
The crankpins of each pair of cranks are in line and the pistons 
connected to them move in unison; the three pairs of cranks 
are 120° apart. 

Crank-shafts for eight- and twelve-cylinder automobile 
engines are practically the same as the crank-shafts for four- 
and six-cylinder engines, respectively, with the exception that 
the crankpins are so proportioned that each can accommodate 
two cylinders instead of one. This is made possible by the 
Y-arrangement of the cylinders by which half the cylinders 
stand at an angle to the other half. 


FLYWHEELS 

33. Object of Flywheel. —A heavy flywheel is neces¬ 
sary for most gas engines, and especially for those of the 
single-acting four-cycle type, in which the piston receives only 
one power impulse in each four strokes. In one of these four 
strokes compression takes place, and the flywheel must store up 
sufficient energy to do the work of compressing the charge. 
The weight of the flywheel depends largely on the number of 
cylinders and the use for which the engine is intended. An 
engine designed to drive a dynamo for lighting purposes must 
run with very little variation of speed, and the flywheel must 
therefore be heavier than a flywheel on an engine intended for 
ordinary shop use or for pumping. Even with a heavy flywheel 
a single-cylinder engine can not be made to run without some 



22 


GAS-ENGINE DETAILS 


slight variation of speed. Consequently, when even running is 
necessary, engines are built with two or more cylinders, so 
that the energy of the impulse is divided. If the engine is to 
run slowly, the flywheel must be correspondingly heavier; the 
higher the speed and the larger the number of cylinders, the 
smaller and lighter may be the flywheel. 

34. Construction of Flywheels. —The aim in design¬ 
ing flywheels is to place the weight as far as possible in the rim 
and to make the hub and arms as light as is consistent with 



strength and safety. In practice, however, this aim cannot 
always be carried out, as the difference in body of metal between 
the rim and the arms may cause severe stresses to be set up 
when the wheel is cast. To relieve these stresses the hub is 
often divided into two parts as shown in Fig. 22 (a). The 
wheel is clamped to the shaft by four strong bolts a which pass 
through the hub b, and the wheel is further secured by a key c. 
This construction is usually adopted for medium and heavy 
flywheels, but very large heavy flywheels are sometimes cast in 


































































GAS-ENGINE DETAILS 


23 


halves and afterwards fastened together at the rim and hub. 
In some cases two bolts are used through a split hub as shown 
in (b) and sometimes the hub is split only on one side and one 
bolt is used as shown in (c). When shrinkage stresses, due to 
casting, are not excessive, as in small flywheels, the hub is cast 
solid and a tapered key is used to fasten the flywheel to the 
crank-shaft. 


VALVES 


35. Inlet and Exhaust Valves. —The inlet and exhaust 
valves used in gas engines are of the mushroom type and are 
known as poppet valves. A poppet valve consists of a disk with 



Fig. 23 


a stem at right angles to the plane of the disk. Poppet valves 
are used for the admission of the charge and the control of the 
exhaust. The valves open in the direction of the axis of the 








































24 


GAS-ENGINE DETAILS 


stems, and are held to their seats by springs. As they open 
inwards, they have no tendency to leave their seats during the 
explosion, the pressure in the cylinder helping to keep them on 
their seats. The valve seats and valve-stem guides may be 
located in removable heads or in the cylinder casting. An 
example of the application of poppet valves to the cylinder of a 

horizontal stationary gas en¬ 
gine is shown in Fig. 23. 
The valve disk d and the 
stem s admit the charge and 
the disk d' and stem s' control 
the exhaust. 

36. The valve seats are 
usually made of cast iron. 
Nickel steel and tungsten steel 
are quite commonly used for 
valves when the head and 
stem are made in one piece; 
nickel steel is also used ex¬ 
tensively for the heads of 
built-up valves having the 
stems made of machinery 
steel. It is claimed that valves 
made of nickel steel will 
neither warp nor scale from 
excessive heat; in addition, 
valves made of tungsten steel seem to be free from pitting. 
Cast-iron exhaust valves having steel stems are sometimes 
used, and also soft-steel valves faced with cast iron welded to 
the head. 

The valve seats are occasionally flat, though more frequently 
they are beveled to an angle of 45°. The bevel-seat type of 
valve is kept tight more easily than the flat-seat type, and for 
this reason it is generally used. 

37. A valve that is opened by mechanical force applied by 
rigid parts is called a mechanical valve, or, less commonly, a 
mechanically operated valve,. An exhaust valve of the poppet 



































GAS-ENGINE DETAILS 


25 


type must always be mechanically operated, because it must 
be lifted against the pressure in the cylinder at the time the 
exhaust is to begin. The inlet valve, however, can be so con¬ 
structed as to be opened by the pumping action of the piston 
during the suction stroke. When thus opened it is known as 
an automatic inlet valve. 

38. A mechanically operated inlet valve for a vertical 
engine is shown in place on its seat in Fig. 24. The disk a 
rests on the beveled seat b and the 
stem c extends downwards through 
the guide d to the adjusting screw e, 
which is not a part of the valve stem, 
however. The valve spring f is held 
in compression between the guide d 
and the cap g, which is held in place 
by a collar h with a radial slot that fits 
in a groove around the stem c. As 
the cam i turns so that its lobe is 
directly under the valve lifter j, the 
valve is raised against the compression 
of its spring and an opening is formed 
between the edge of the valve and the 
seat. The valve lifter j by suitable 
means is prevented from turning in 
the valve-lifter guide k, and can be 
adjusted by screwing the adjusting 
screw e up or down. A locknut l pre¬ 
vents the adjusting screw from turning out of adjustment. In 
the center of the top of the valve disk is a slot to receive the 
end of the tool used when grinding the valve. Frequently the 
spring cap is held in place by means of a key that passes 
through a hole in the valve stem, instead of by a slotted collar. 

39. A mechanically operated inlet valve and cage for a 
vertical stationary engine is shown in Fig. 25. The valve a is 
shown in place on its seat b which is carried by the cage c. The 
valve stem d is guided at one end by the bushing e, which is 
fitted in the cage, and at the other end by the guide piston / 



















2G 


GAS-ENGINE DETAILS 


which is a working fit in the upper part of the cage. In order 
to fasten the valve stem to the guide piston, the valve stem is 
grooved near the top end, as shown, to receive a split ring g, 
which, when in place, fits into a recess in the piston. A liner h 
is clamped tightly between the top end of the valve stem and 
the inside of the socket nut i so that the pressure on the top 
of the socket nut from the valve lever, which is not shown, is 
transmitted directly to the inlet valve. The outer spring j is 
the valve spring proper which returns the valve to its seat, and 
the inner spring k serves as a buffer to cushion and arrest the 
motion of the valve in case of back fires. The charge is taken 

into the cylinder, when the 
valve is open, through the 
port l in the side of the valve 
cage. 

40. The principle of opera¬ 
tion of an automatic inlet valve 
is shown in Fig. 26. The valve 
stem a works in a guide b, 
which is connected by a three¬ 
armed spider to the shoulder 
cage c, against whose base the 
valve head d seats. A gas- 
tight fit between the valve d and 
its seat is secured by grinding. 
The shoulder e is carefully 
machined, and fitted against an internal shoulder in the cylin¬ 
der head, the joint being practically gas-tight. In the center of 
the valve head is a slotted boss f, to receive a screwdriver for 
turning the valve for grinding. A thin nut g, backed by a 
cotter pin h, retains the spring. As it takes a little time to 
unscrew this nut, a washer is sometimes used in its place and 
is retained by a thin flattened key slipped through a narrow slot 
in the valve stem. The key is so formed that by compressing 
the spring slightly it is readily slipped out, but cannot otherwise 
escape. 




















GAS-ENGINE DETAILS 


27 


VALVE MECHANISM 

41. Valve Springs.— Springs for valves are usually 
made from steel spring wire or from soft cast-steel wire, the 
former being wound cold and not requiring any heat treatment; 
when the soft wire is used, the spring is hardened and tempered 
after it is formed. Springs made from spring wire have the 
disadvantage of becoming set if subjected to hard usage, and 
hardened and tempered springs are liable to break if not 
tempered just right. 

Helical springs, or springs wound in the form of a screw 
thread, are used more often than any other. Occasionally, the 
springs on inlet and exhaust valves 
are made up in the shape of a 
cone. Such springs are called 
conc-shapcd springs. 

42. When the inlet and ex¬ 
haust valves are interchangeable, 
and hence are mechanically oper¬ 
ated, the tension of the springs is 
unimportant as long as it is suffi¬ 
cient to seat the valves. The 
amount of tension on the springs 
of automatically opened inlet 
valves is, on the other hand, an im¬ 
portant matter. To get the great¬ 
est amount of power from an 
engine having an automatically operated inlet valve, the spring 
must be carefully adjusted to insure the required opening of 
the valve when in operation. In adjusting the tension of the 
inlet-valve spring, it is necessary to be careful that nothing is 
accidentally dropped into the cylinder and to make sure that 
the nut or pin holding the inlet-valve spring does not become 
loose, especially if the valve is of the inverted type. 

43. Cam-Shafts. —On horizontal stationary gas engines 
the cam-shaft, sometimes called the side shaft, lay shaft, or 
two-to-one shaft, is usually at right angles to the crank-shaft 



356—3 




28 


GAS-ENGINE DETAILS 


and is driven from it by means of spiral gears as shown in 
Fig. 27. The crank-shaft c carries a spiral gear G, which is 
essentially a short screw having a large number of threads. 
This gear meshes with the spiral gear g on the cam-shaft v. 
The number of teeth on this gear is double the number on the 
gear G, so that the shaft c makes two revolutions to one of the 
shaft v that it drives. From the cam-shaft, the valves them¬ 
selves are operated by cams. If the cam-shaft is driven by 
spur gears, as is commonly the case in vertical stationary, auto¬ 
mobile, aviation, marine, and tractor engines, the cam-shaft is 
parallel with the crank-shaft. In automobile engines the cam¬ 
shaft is sometimes driven by means of a silent chain. 

44. Operation of Valves. —In order to lift the valves at 
the proper time and to keep them open for the correct period, 





(b) (o 

Fig. 28 



cams are generally used on gas engines, except in the largest 
sizes of stationary engines, where eccentrics are sometimes 
used. Cams vary considerably in shape, or profile, the outline 
depending somewhat on the type of contact-piece, or cam-fol¬ 
lower, which is the part of the valve-operating mechanism that 
is in contact with the cam. An inlet-valve cam designed to be 
used with a roller follower is shown in Fig. 28 (a), and the 
corresponding exhaust-valve cam is shown in (b). Another 
common form of cam, also used with a roller follower, is 
shown in (c). The cam shown in (c/) has rising and falling 
shoulders a and b of convex form, giving a gradual opening and 
closing. This form of cam is used with a flat contact-piece, or 
follower. The cams may be secured to the cam-shaft by keys, 
taper pins, or screws, or by combinations of these, but in many 
cases the cams are forged .on the cam-shaft. 


GAS-ENGINE DETAILS 


29 


45. The use of cams for operating the valves of a sta¬ 
tionary gas engine is illustrated in Fig. 29, which is a section 
of the engine through the cylinder and valve mechanism. To 
the side, or cam, shaft a, which is driven from the main shaft 
by means of a pair of spiral gears, are keyed the cams f and b 
for operating the valves. The cam b operates the exhaust 
valve c by means of the valve lever, or rocker-arm, d, which 
is supported by a bearing at e. The cam / opens the inlet 
valve g by means of the rocker-arm h, which is pivoted in a 
bearing i, and the ad¬ 
justable push rod j. 

The cam-follower, or 
roller, k is held in a 
yoke which is free to 
move about the piv¬ 
ot /. A roller cam- 
follower m is also 
used on the rocker- 
arm for operating the 
exhaust valve. 

46. The valves of 
large stationary en¬ 
gines are usually oper¬ 
ated by eccentrics 
instead of cams. The 
eccentrics are keyed 
to the side shaft in 
the same way as 
cams and, as a general rule, give more quiet operation, without 
shocks. Eccentrics are more costly than cams but they have a 
larger wearing surface and give a smoother action to the valves 
which makes them more desirable for large engines. Both the 
inlet and the exhaust valves are usually operated by means of a 
rocker and wiper-cam arrangement which is driven by pull rods 
attached to a common eccentric. 



Fig. 29 













30 


GAS-ENGINE DETAILS 


MISCELLANEOUS ENGINE FITTINGS 

47. Priming Cups. —A cock by means of which an 
engine may be primed by pouring fuel into the combustion 
chamber, and which may also be used to relieve the compres¬ 
sion, is shown in Fig. 30. It consists of a circular plug a 
carefully ground to fit the tapering, or conical, socket in which 
this plug is turned by means of the handle b. The cup c is 
sufficiently large to hold the required amount of gasoline for 
the priming charge when the engine is to be started. The 

plug a is held in place by a phosphor- 
bronze spring d placed between two 
washers e and f, and a pin g serves to 
hold the whole together. The tension of 
the spring d is sufficient to hold the plug 
firmly in position and to take up wear, 
thus preventing lose of compression by 
leakage. The spring also serves to keep 
the plug tight under heavy vibration. In 
using this plug, the gasoline for prim¬ 
ing is poured into the cup c and the 
cock a is turned so as to permit the 
gasoline to flow into the cylinder either before the engine is 
started or during the suction stroke. 

Priming cups are also used for introducing kerosene or any 
other similar substance into the cylinders for the purpose of 
keeping down carbon deposits. 

48. Joints. —In order to prevent leakage at the joints of a 
gas engine, a packing, or gasket , is usually placed between the 
two parts forming the joint. The materials used in making 
joints are usually copper, lead, asbestos, brown paper, wire 
gauze, etc., or combinations of these materials, the copper 
asbestos combination being most used. Gaskets containing 
rubber should never be used around a gasoline engine or in 
gasoline-supply piping, because rubber is more or less soluble 
in gasoline. In the water-supply and water-discharge piping, 
rubber gaskets or packing .are frequently used, but it is much 



Fig. 30 








GAS-ENGINE DETAILS 


31 


better to use ground-joint unions, that is, unions in which the 
joint is made by metal surfaces ground together. This form 
of joint is also used in gasoline piping, where gaskets of any 
description are dangerous. A gasket material composed 
largely of brass-wire gauze and asbestos is much used for joints 
that are subjected to high temperatures. When properly fitted 
and provided with graphite facing, such a gasket will, with 
care, last a long time. Combined copper and asbestos ring 
gaskets are also well adapted for use in recessed places, under 
inverted inlet valves, screw plugs, valve bonnets, etc. This 
form of gasket consists of compressible, elastic packing encased 
in soft-rolled copper, which makes a lasting joint under high 
pressures and temperatures. 

49. Fastenings.—Bolts should be used for fastening the 
different parts of the gas engine together whenever a strong 
joint is desired, unless the construction of the part is such that 
this cannot well be done. The reason for this is that it is much 
easier to split and remove a rusted nut from a bolt than to drill 
out the rusted end of a capscrew that has been twisted off 
when trying to remove it from the part into which it was 
screwed. 

Capscrews and tap bolts have a thread on one end and a 
hexagonal head on the other. They are sometimes used where 
it is difficult or impossible to use a bolt and a nut. Where two 
parts are to be fastened by a capscrew, a hole is drilled through 
one and a smaller hole drilled and tapped into the other. The 
parts are put together, and the capscrew passed through the 
larger hole and screwed into the tapped part. 

Setscrews are used for fastening collars or couplings to 
shafts, or for fastening other temporary connections. The 
heads are often square, but are sometimes of other shapes. 
The points may be conical, flat, ball-shaped, or cup-shaped, 
so that when screwed into place they prevent the parts from 
slipping. The shaft should have a small depression where the 
setscrew strikes it, so that the setscrew will hold better with¬ 
out causing a burr to be formed on the shaft. The heads of all 
projecting screws in revolving machinery should be covered by 


32 


GAS-ENGINE DETAILS 


a guard, so as to prevent the possibility of accidents to any 
person through catching the clothing on such projections while 
the machinery is in motion. 

Stud bolts are rods of wrought iron or steel with threads 
cut on both ends; one end is screwed permanently into some 
part of the engine to hold in place another part—such as, for 
example, a brace, a cylinder head, or a valve cage—by means 
of a nut screwed on the other end of the stud bolt. As the 
parts into which these stud bolts fit are frequently made of 
cast iron, they sometimes rust solid; but constant removal of 
the loose parts tends to destroy the threads on the free ends 
of the stud bolts and hence to produce trouble from leakage. 
They should be used in preference to capscrews wherever 
possible. 

Spring* cotters, or split pins, are necessary on bolt or 
stud nuts to prevent them from jarring loose and from work¬ 
ing off entirely. They should be used wherever loose bolts or 
nuts are liable to prove harmful. 

50. Collars.—In order to prevent or limit endwise motion 
of revolving or reciprocating parts collars are generally used. 
They are either solid or split. Solid collars may be held in 
position by setscrews, taper pins, or other means, or they may 
be used loosely on shafts to keep other parts at a distance. 
Split collars are made in halves and are held together by pins 
or screws. While they are not so strong as the solid pattern, 
they are frequently very convenient and often used in gas- 
engine practice. The split collar has the advantage over the 
solid form in that it can be put into place anywhere in a space 
equal to twice its width, while the solid form must be slipped 
over the end of the part on which it is to be fastened. 


GAS-ENGINE LUBRICATION 

Serial 1860 - Edition 1 

PURPOSE AND NATURE OF LUBRICANTS 


FRICTION AND LUBRICATION 

1. No matter how smooth a metallic surface may seem to 
the sight or to the touch, it is in reality covered with very 
minute projections, so that the surface consists of ridges and 
hollows. These may readily be seen under a microscope. 
Thus, when two clean metallic surfaces are placed together, 
and motion is given to one or both of them, so as to cause one 
to slide or roll on the other, the little ridges engage one another, 
or interlock, so that there is a resistance to the motion. This 
resistance is called friction. The amount of friction depends 
on the pressure with which the two surfaces are held together, 
the materials of which the surfaces consist, and the condition 
of the surfaces. The movement of one surface over the other 
causes some of the small ridges to be broken off or torn loose 
from each surface. This tearing away or abrading of the 
metal is called wear. 

2. Lubrication consists in introducing some substance, 
either liquid or solid, between two rubbing surfaces, to reduce 
the friction and the wear that would otherwise occur. The 
substance used, which may be oil, grease, graphite, or com¬ 
binations of these materials, is known as the lubricant. 
When it is put between the two surfaces, it spreads out and 
forms a thin layer, or film, that fills up the very small hollows 
in the surfaces and so prevents the metals from touching each 
other except at the points of the highest ridges. As a conse- 


COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ALL RIGHTS RESERVED 




2 


GAS-ENGINE LUBRICATION 


quence, fewer ridges can interlock, and so less effort is needed 
to move one surface over the other; in other words, the friction 
is decreased. As fewer ridges are broken off or torn loose, 
the wear is correspondingly lessened. 


LUBRICANTS 


OILS 

3. The lubricants most extensively used are oils, although 
they are often adulterated with other substances to produce 
or increase certain properties, such as viscosity, fluidity, 
weight, etc. The viscosity of an oil is a measure of the 
ease with which it flows. A very viscous oil, or one that 
has high viscosity, flows very sluggishly; on the other hand, if 
the viscosity is very low, so that the oil flows rapidly and freely, 
the oil is said to be fluid, or to possess fluidity. The oils that 
are used as lubricants may be obtained from animal, vegetable, 
or mineral sources. 

4. The animal oils that are most commonly used for lub¬ 
ricating purposes are tallow, lard oil, neat’s-foot and sperm oil. 
These are commonly called fat, or fixed, oils because they do 
not volatilize when heated to moderate temperatures. As 
they are of animal origin, they are liable to become rancid, in 
which condition they are unfit for use; otherwise, they are 
excellent lubricants, but they are usually too expensive for 
general use. 

5. There are two oils that are of mineral origin, namely, 
shale oil which is obtained from certain shales, and mineral oil, 
which is obtained from oil wells. Shale oil is not of much 
value as a lubricant and it will therefore not be considered 
further. Mineral oil as it comes from the wells is called 
crude oil. When it is heated, vapors are given off, which, 
when condensed, form various lighter oils that are called 
distillates. Among the distillates thus obtained are various 
lubricating oils. The heating of crude oil to a temperature but 
slightly above that of the atmosphere drives off vapors that 




GAS-ENGINE LUBRICATION 


3 


form gasoline when they are condensed. A somewhat higher 
temperature drives off vapor that forms kerosene, and so on. 
Each increase in temperature drives off a different oil from 
those that have preceded and each oil is less fluid than the one 
that was obtained before it. After kerosene, a number of oils 
that are used for lubricating purposes are obtained. When the 
lighter elements have been driven off, the residue is drawn off, 
and is passed through a strainer to free it from grit and earthy 
matters. It is afterwards cooled and the wax removed. Heavy 
bodied oils, including steam-engine cylinder oil, are made 
largely from this residual product. Many cylinder oils for use 
in internal-combustion engines consist of combinations or 
blends, of distillate with the heavier residual stocks in varying 
proportions. Some lubricating oils are comparatively thin 
whereas others are quite thick. All lubricating oils increase in 
fluidity when their temperature is raised; that is they lose 
their body, or decrease in viscosity. 

6. The thickness, or body, of an oil, commonly called its 
viscosity, is an important property in lubricating. The lower 
the viscosity—that is the thinner the oil—so long as other con¬ 
ditions are satisfied, the better the oil for lubricating purposes. 
Some oils become so thin at high temperatures that they lose 
most of their lubricating properties. Mineral oils, when heated, 
lose their viscosity much more rapidly than animal or vegetable 
oils, but vegetable and animal oils burn more easily. 

Mineral oils give off inflammable vapors when heated. The 
amount of these vapors is at first not sufficient to ignite, but at 
a certain temperature enough is given off to ignite with a flash, 
though the flame dies out almost immediately. The tempera¬ 
ture at which the flash appears is called the flash point. Vapor 
is given off in sufficient amount to maintain a flame constantly 
when the temperature is raised somewhat above the flash point. 
This temperature is called the burning point. An oil is said to 
have a high fire-test or a low fire-test according as the burn¬ 
ing point is high or low. The higher the viscosity of an oil, 
the higher is its fire-test. The fire-test of lubricating oil should, 
therefore, be as low as is consistent with safety under service 


4 


GAS-ENGINE LUBRICATION 


conditions. When the flash point of an oil is 300° F. or 
higher, there is little danger of fire when handling it under 
ordinary circumstances. Oils that flash at a temperature much 
below 300° F. give off, at atmospheric temperature, inflammable 
vapors that increase the fire risk if the oil is stored where there 
is not free ventilation. The loss by evaporation is also greater 
from an oil of low fire-test than from one having a high fire- 
test. Lubricating oils do not, as a rule, flash at a temperature 
below 300° F., and they therefore do not offer very great 
danger of fire. 

7. Cylinder Oil. —There are three essential properties 
that a good gas-engine cylinder oil must possess. 

1. It must have as high a fire-test as practicable; that is, 
the temperature at which it gives off inflammable vapor should 
be as high as is consistent with the desired body. In the best 
gas-engine cylinder oils, this temperature will be about 450° F., 
which gives a satisfactory factor of safety, inasmuch as the 
temperature of the cylinder walls of internal combustion 
engines rarely rises above 250° F. 

2. It must be of the best quality; that is, it should leave as 
little residue as possible when the oil is vaporized by heat. Any 
cylinder oil will leave some carbon deposit, which gradually 
accumulates on the inner walls of the combustion chamber and 
on the piston head and valves, but it is desirable that this 
accumulation should be prevented as far as practicable. If it 
becomes thick, especially if the compression is high or if the 
form of the combustion chamber is such that sharp corners are 
exposed to the heat of the flame, particles of the unburned 
carbon clinging to the walls or elsewhere may become heated to 
such a degree as to ignite the charge before compression is 
complete. 

3. The third requirement of a good gas-engine cylinder 
oil is that it shall have the proper body. If the oil is too heavy, 
it will not work past the piston rings in sufficient quantity, while 
if it is too light, the high temperature of the cylinder will 
reduce its viscosity and make it too thin to be used satisfac¬ 
torily as a lubricant. 


GAS-ENGINE LUBRICATION 


5 


8. It is often advisable to use oil of different characteristics 
in an automobile engine than is necessary in a stationary engine, 
because of the greater rapidity of the explosions in the auto¬ 
mobile engine and the consequently higher internal tempera¬ 
ture. As it is hard to get at the combustion chamber to scrape 
the carbon deposit from it, it is well to use an oil that leaves as 
little deposit as possible. For air-cooled cylinders, only the 
heaviest oil obtainable and with the highest possible fire-test 
should be used, and the oil tank should be placed near enough 
to the cylinder or exhaust pipe to insure that the oil will feed 
readily in cold weather. 

9. Grade of Oil. —For water-cooled engines of the high¬ 
speed type, such as are used in automobile and aeroplane ser¬ 
vice, the grade of cylinder oil known as medium is appropriate 
for summer use. In weather cold enough to cause this oil to 
stiffen, the next lighter grade, or light, may be employed. 
In cold weather, if the light oil does not feed freely, it is best 
to use a special oil suitable for use at low temperatures, though 
it is possible to thin the regular oil with kerosene or gasoline, 
to make it flow, and to increase correspondingly the feed of the 
oil cup or mechanical lubricator. It is best in every case to 
purchase oil that is known to be reliable. Besides, most manu¬ 
facturers of automobiles recommend certain oils for use in 
their engines. These oils may always be used with confidence 
in any engine of about the same character as that for which 
they are put up. 

10. Should it be found impossible to obtain oil that is 
known to be suitable, the samples available may be tested for 
viscosity by putting a few drops of each on an inclined sheet of 
clean metal or glass, and noting the relative rapidity of their 
downward flow. The one that flows most rapidly has the least 
or lowest viscosity, and the one that flows most slowly has the 
greatest or highest viscosity. The oils may be tested roughly 
for flashing point and for the carbon residue they leave by 
putting a little on a sheet of iron or tin plate, and heating 
gradually over a flame, care being taken to move the plate over 
the flame so that all parts of it are evenly heated. The oils 


GAS-ENGINE LUBRICATION 


will become less viscous and will run on the plate, and for this 
reason two samples compared at the same time should not be 
placed too close together. They will gradually vaporize, leav¬ 
ing only a brownish and somewhat thick residue, which should 
be as small in amount as possible. A good, heavy oil will 
vaporize almost completely, but will retain considerable body 
even at temperatures where an oil of low fire-test would be 
entirely burned away. Oils, either heavy or light, that leave 
any considerable amount of black, tarry residue should be 
avoided. 


11. Although, strictly speaking, cylinder oil needs to be 
used only for cylinder lubrication, the same oil is generally 
used for all bearings of the motor. This is particularly true of 
automobile engines, where the oil supply is carried in the 
crank-case and used for the lubrication of the bearings as well 
as the cylinders. Cylinder oil is an excellent lubricant for 
bearings subjected to hard service, as those of the crankpins 
and crank-shaft, but, when possible, better service can be 
obtained by supplying each bearing with an oil that is par¬ 
ticularly suited to its working conditions. 


GREASES 

12. There are cases in which the use of oil as a lubricant is 
either inconvenient or impossible, and under such circumstances 
grease is commonly used. Grease is generally made by adding 
a soap to lubricating oil, thus thickening it. The thickness of 
grease varies from the consistency of a thick liquid to that of a 
hard soap. The harder grease contains more soap than the 
soft grease. The lubricating properties of a grease are not 
usually available for the reduction of friction in a bearing until 
the temperature of the bearing has become sufficiently high to 
melt the soap and thus liberate the oil contained in the grease. 
The soap adds little, if anything, to the lubricating properties 
of the grease. 

Mineral oil is commonly used in grease, the soap used for 
thickening it being either a tallow soap or a mineral soap. The 



GAS-ENGINE LUBRICATION 


7 


tallow soap is made of tallow or other suitable fat which is 
commonly saponified by the addition of potash, and it is there¬ 
fore sometimes called a potash-tallow soap. Some of the 
vegetable oils, such as olive, rape-seed, and cotton-seed oils, 
may be saponified by such alkalies as lime, soda, and potash. 
In mineral greases, a mineral soap such as aluminum soap is 
used. 


13. Since a grease must melt before the lubricant is avail¬ 
able, a grease that melts at a temperature sufficiently low to 
keep the bearing from being damaged must be chosen. Grease 
melts at temperatures varying from about 75° F. to 150° or 
200° F. The melting temperature depends both on the amount 
of soap in the grease and on the kind of soap. The flash point 
and the fire point of a grease are usually the same as those of 
the oil contained in it. 

Both grease and oil are frequently used in places where the 
temperature around the bearing is very high or very low. 
When the temperature of the surrounding air is high, a grease 
suitable for use in the bearing must have a melting point only 
slightly above that of the air, in order that the bearing will 
not become too hot before the grease melts. Furthermore, if 
oil, by itself, is employed, neither it nor the oil used in the 
grease should flash at a temperature less than 100° above the 
air temperature. If the bearing is exposed to very low tem¬ 
peratures, a grease of such consistency that it will not become 
hard at the temperature of the air must be used. 

Solid materials such as graphite and soapstone are some¬ 
times added to grease to harden it. Graphite also adds valuable 
lubricating qualities to the grease or oil with which it is mixed, 
providing the graphite is not used in such quantities as to 
make a mud and clog the bearing. Graphite smooths the sur¬ 
faces of the bearing by filling up the hollows and thus reduces 
both friction and wear. 

14. Automobile Greases. —The greases used in auto¬ 
mobile work are made in different consistencies to suit different 
climatic conditions and service. As a general rule, each brand 


8 


GAS-ENGINE LUBRICATION 


of grease is made in three consistencies, often known as hard, 
medium, and light grease, although some makers manufacture 
five consistencies and give each an identification number. A 
distinction is usually made between cup greases, which are 
intended to be used in compression grease cups, and transmis¬ 
sion greases, which are often called non-fluid oils. Transmis¬ 
sion greases are very soft and fluid and, as implied by their 
name, are intended to be used in automobile transmissions and 
rear-axle housings to furnish a suitable lubricant for their 
gears and bearings; they are entirely too fluid to be used in 
grease cups. 

The viscosity of many cup greases is greatly affected by the 
temperature to which they are subjected, the greases becoming 
more fluid as the temperature rises and less fluid as it becomes 
lower. With such greases, a hard grade should be employed 
in summer, a medium grade in the spring and fall of the year, 
and a light grade in winter, in order that the grease may be fed 
freely from the grease cups. Some cup greases are affected 
but little by temperature changes, and then the same grade may 
be used all the year around. 

The use of grease in transmissions and rear axles is not as 
common now as formerly, many automobile manufacturers 
recommending the use of a heavy, steam-engine cylinder oil 
instead. Ordinary, cheap, steam-engine cylinder oil is of little 
value as a lubricant for transmissions and rear axles; best 
results are usually obtained from a cylinder oil suitable for 
superheated steam and having a fire-test of about 600° F. 

15. Some transmission greases are of a fibrous nature and 
cling to the gears with great tenacity; better results are usually 
obtained from such greases than from greases that are so fluid 
that they will drip at once from the gears. Greases that are 
so heavy that the gears simply cut a path through them are of 
no value in transmissions, etc.; by mixing them with gas-engine 
cylinder oil, however, their consistency can often be reduced so 
that they will give satisfactory service. A transmission grease 
that is too light to cling to the gear-teeth can be thickened by 
mixing it very thoroughly with a sufficient quantity of heavy 


GAS-ENGINE LUBRICATION 


9 


cup grease. As a general rule, however, it will be more satis¬ 
factory to use a transmission grease of the right consistency 
than to attempt to obtain it by mixing as just described. 


LUBRICATING SYSTEMS AND DEVICES 


LUBRICATING FILM 

16. The lubricant that is introduced between two bearing 
surfaces should form a film sufficiently thick to keep the sur¬ 
faces separated. The pressure between the bearing surfaces 
tends to break the lubricating film down and to squeeze the 
lubricant out. The lubricant should therefore have a sufficient 
viscosity to maintain itself in the bearing. If a shaft carrying 
a weight revolves in a bearing, it tends to roll up on one side of 
the bearing so that the point of greatest pressure is a little to 
one side of the bottom of the bearing and the point of least 
pressure is diametrically opposite the point of greatest pressure. 
The lubricant tends to squeeze out at the point of greatest pres¬ 
sure, therefore it should be introduced at the point of least 
pressure, so that the revolving shaft will continuously carry a 
fresh supply of oil to the part of greatest pressure. If an oil 
has too little viscosity, the film of oil will break down and allow 
the metallic surfaces to come together. The bearing will then 
heat and it may be damaged. On the other hand, an oil may be 
too thick to enter the space between the surfaces of the bearing. 
The proper oil will, however, be carried into the bearing by the 
movement of the shaft so that the two surfaces are separated 
by a film of oil. There are four general systems of supplying 
oil to bearings. They are the gravity system, the splash system, 
the force-feed system, and the combination system. 


GRAVITY SYSTEM 

17. In the gravity system of lubrication, the oil supply 
is contained in a cup or tank placed above the bearing. Some¬ 
times the cup supplies oil for only one bearing and in other cases 





10 


GAS-ENGINE LUBRICATION 


for a number of bearings. One of the simplest forms of gravity 
system is shown in Fig. 1. It consists of a cup a fitted with a 
c central tube b and a removable cover c< 

The oil contained in the cup is led into 
the central tube by capillary attraction, a 
few strands of lamp wick, shown at d, 
carrying the oil over. The advantage of 
this oiling device is its simplicity; the 
disadvantages are its unreliability and its 
lack of adjustment of the oil feed. The 
latter can be adjusted to some degree by 
changing the number of strands of lamp 
wick; as the flow of oil is not in plain 
sight, however, there is always some 
doubt about the action of the lubricator. 



18. The sight-feed lubricator, shown 
in Fig. 2, permits the regulation of the oil supply and the 
observation of the rate of flow. The glass cup a contains the 
oil, which flows out through the small hole at the lower end of 
the tube b. The amount of oil flowing to the 
bearing is controlled by a needle valve inside 
of the tube b. The needle valve is adjusted 
by the screw c which is set and locked in any 
desired position by the locknut d. The rate 
of feeding the oil to the bearing is visible in 
the sight-feed glass e . The cup may be 
filled through the hole in the top, which is 
then closed by the cover /. 

The sight-feed oiler, shown in Fig. 3, is 
intended for use on gas-engine cylinders. In 
case of an excessive back pressure from the 
cylinder, the brass ball a will be raised against 
the seat above it, thus closing the passage. If 
the back pressure is not high enough to lift 
the ball, the gases will pass up through 
the tube b, which extends above the surface of the oil, per¬ 
mitting the pressure to be equalized. The lever c when down, 



Fig. 2 



























GAS-ENGINE LUBRICATION 


11 


closes the needle valve that regulates the feed, and the cup can 
easily be filled by sliding the cover d 
lever c is in a vertical position, the cup 
is feeding; the feed extending well 
into the large sight-feed glass e pre¬ 
vents the oil from adhering to or 
clouding the glass. The amount of 
feed is regulated by the thumb nut f, 
held in place by the spring g. 

19. A number of bearings may be 
oiled from one source, by means of an 
oiler such as shown in Fig. 4, which 
consists of an oil tank provided with a 
number of sight feeds. The oil tank 
is sometimes divided into two com¬ 
partments, one of which may be used 
for cylinder oil and the other for bear¬ 
ing oil. Two filler holes are then pro¬ 
vided, one for each compartment. The 
end a of the tank is made of glass, so 
that the level of the oil is readily visible, and a sight-feed 
outlet b is provided for each bearing and the flow of oil is 

controlled by the cam 
levers c in exactly the 
same way as in Fig. 3. 
Sometimes the sight feeds 
are provided with check- 
valves so that any of them 
can be used for the lubri¬ 
cation of the gas-engine 
cylinder; in other cases, 
only the sight feeds lead 
ing from one of the two compartments are provided with 
check-valves. Feeds that are provided with check-valves are 
always fitted with equalizing tubes to equalize the pressure 
above and below the oil in the reservoir. 



Fig. 4 



356—4 

















12 


GAS-ENGINE LUBRICATION 


FORCE-FEED SYSTEM 

20. In the force-feed system of lubrication, the required 
amount of oil is pumped to each bearing under a pressure suffi¬ 
cient to force the oil into the bearing. If there is little resis¬ 
tance to the passage of the oil, the pressure will not be high, 
but it will always be high enough to force a fixed quantity of 
oil into the bearing. The oil tank of a force-feed lubricator 
contains at least one pump for each bearing that is to be oiled. 
A pump such as is used for this purpose is shown in Fig. 5. 

The shaft a in the upper 
part of the oiler is rotated 
by the engine through the 
ratchet wheel b. Each oil 
pump, only one of which is 
shown, is driven by an ec¬ 
centric c that is set at an 
angle on the shaft. The 
yoke d drives the pump 
plunger e which fits in the 
barrel /. Oil is delivered 
through the passage g to 
the pipe, not shown, at¬ 
tached at h, that leads to 
the bearing. The check- 
valve i prevents the oil from 
being forced or drawn back 
into the oiler, and the test 
plug j may be opened to see 
whether the oiler is work¬ 
ing ; but when the test plug 
is opened, no oil is delivered to the bearing. As the eccentric c 
is askew on the shaft, the plunger e has a rotary as well as an 
up-and-down motion. There is a slot k that registers with the 
opening to the passage g during the downward stroke of the 
plunger. The plunger is turned, when near the bottom of its 
stroke so that the slot k comes opposite the hole l, shown dotted, 
in the pump barrel, through which oil is then drawn during the 













































GAS-ENGINE LUBRICATION 


13 


upward stroke. At the top of the stroke, the slot k is turned 
back to the discharge opening. The eccentric is constructed so 
that the stroke of the pump can be adjusted to deliver the 
required amount of oil. Such an oiler can be fitted with sight 



feeds but the benefits of the force feed to the bearing are then 
lost, as the oil must flow by gravity from the sight feed to the 
bearing. 


21. An oiler that has sight feeds and force feed to the 
bearings used on stationary engines is shown in Fig. 6. The 






































































14 


GAS-ENGINE LUBRICATION 


grooved pulley a is driven by a belt from any convenient shaft 
connected with the engine, and turns the worm b and worm- 
wheel c, the latter being mounted on the shaft d. Secured to 
this shaft are eccentrics e, whose number is one greater than 
the number of bearings to be supplied. These eccentrics work 
in oval-shaped yokes f that are guided by the square stems g 
above, which prevent the yokes from turning, and are con¬ 
nected below to the pump plungers h. One of these plungers, 
not shown, has a cross-section equal to all the others combined, 
and lifts the oil from the main reservoir i to the auxiliary 
reservoir, or oil space j. This oil space is separated from the 
chamber i by a partition, and if more oil is supplied to the oil 
space than the bearings take, it overflows into the chamber i. 
From the reservoir j, the oil flows down past the adjustable 
needle valves k, one for each bearing supplied, to and through 
the sight feeds l, and then to each pump barrel through the two 
ball check-valves m, the first a very small one working horizon¬ 
tally and closed by a spring, and the second working vertically 
and located directly under the plunger h. 

22. On the down stroke of the plunger, the oil passes out 
through a passage shown by the dotted lines, and through the 
two small check-valves n, Fig. 6, each closed by a spring. The 
object of using two check-valves instead of one, both before 
and after the pump is reached, is to maintain the action of the 
pump, even if one valve should be put out of action by a particle 
of foreign matter. In case this occurs, the other check-valve 
will continue to act until the particle has been dislodged and 
passed on with the oil. 

The oil pumps h are proportioned so that they can pump all 
of the oil that will pass through the needle valves and it is 
therefore impossible for oil to collect in the sight feeds. The 
oil feed may be shut off from any bearing at will, independently 
of the rest, by turning the cam-lever o into the horizontal posi¬ 
tion, thus closing the needle valve connected to it. Owing to 
the great reduction of speed produced by the use of the worm b, 
the action of the pump is very slow. It is, however, propor¬ 
tional to the speed of the..engine, and in this respect the 


GAS-ENGINE LUBRICATION 


15 


mechanical lubricator has an important advantage, since the 
average requirement of oil is roughly proportional to the 
engine speed. 

23. An oiler having the sight feeds on top of the oil reser¬ 
voir is shown in section in Fig. 7. This oiler is provided with 
as many oil-feeding units as there are bearings to be oiled, but 
in Fig. 7, only one unit 
is shown. The shaft a 
which extends through 
the oil reservoir b is 
rotated from a moving 
part of the engine 
through the ratchet 
wheel c. An outside 
crank is provided by 
which the oiler may 
also be operated by 
hand. Each oiling unit 
contains pump plungers 
d and e, which are con¬ 
nected by a yoke /, and 
are driven by the ec¬ 
centric g through the 
crosshead li and the 
rod i. The plunger d 
raises the oil from the 
reservoir b } through a 
strainer, the pipe o, and 
ball valves to the sight 
feed j. From the sight 
feed, the oil is drawn 
by the plunger e through the passage k and delivered to the 
discharge pipe /, whence, it is carried to the bearing through 
suitable connections. 

The amount of oil supplied to each bearing is regulated by 
the position of the nuts m. When they are in the position 
shown, the stroke of the plungers will be equal to the throw of 





























































16 


GAS-ENGINE LUBRICATION 


the eccentric g, but when the nuts are raised so that there is a 
space between them and the end of the arm n that is carried by 
the rod i and operates the plungers, the stroke of the plungers 
will be less than the throw of the eccentric. The greater this 
space, therefore, the less oil will be pumped. 


COMBINATION SYSTEMS 

24. There are a number of lubricating systems that re¬ 
semble one or another of the systems just described, but that 
include some different and distinctive features. For example, 
the system of ring oiling applied to the bearing shown in Fig. 8 



(a) and (b) is a gravity-feed system in which the oil is supplied 
continuously from the oil chamber a by rings on the shaft. As 
the shaft b rotates, the ring c rolls over the top of the shaft, 
and the oil that adheres to the ring is thus carried up on the 
top of the shaft, from which point it is carried by the shaft to 
the bearing. Oil is supplied to the chamber a through the 
cup d. After leaving the surface of the journal, the oil flows 
down the end surface of the bushing e into the circular 
grooves f, and through the ports g back into the chamber a. 
When the oil becomes unfit for further use, the chamber is 
drained through the cock h. A glass gauge i indicates the 
amount of oil contained in the oil chamber. 




















































GAS-ENGINE LUBRICATION 


17 


25. Oil is frequently carried to the crankpin by centrifugal 
force. This method of crankpin oiling is shown in principle in 
Fig. 9. Oil from the sight-feed oiler flows through the tube a 
to the inside of the oil ring b, which is fastened to the face of 
the crank c. Centrifugal force then drives the oil out through 
the tube d and the holes e to the crankpin bearing. 

26. Automobile and traction engines are usually built so 
that the oil drains from the various bearings into a common 
drip tank or reservoir 
placed below the low¬ 
est bearing. A pump 
driven by the engine 
draws oil from this 
reservoir and forces it 
to the various bear¬ 
ings. Sometimes the 
discharge from the 
pump is taken to a 
sight glass placed 
above the engine and 
in plain view of the 
operator. The oil 
flows by gravity from 
the sight glass to the 
various bearings. In 
this system of lubri¬ 
cation not much at¬ 
tempt is made to 
regulate the amount of oil supplied to the various bearings 
except to see that it is ample to prevent unnecessary heating 
and wear. When this system of lubrication is used, the oil 
gradually accumulates more or less dirt and small particles of 
metal so that it must from time to time be replaced with fresh 
clean oil. 

27. Large stationary gas engines are sometimes lubricated 
by a system resembling the one just described but to which are 
































18 


GAS-ENGINE LUBRICATION 


added some features that are not adaptable to automobile and 
tractor conditions. The drips from all bearings are collected 
in a receiver, placed below the lowest bearing, from which they 
are pumped to the top of a filter tank. During its passage 
through the filter tank, the oil is filtered and cooled, so that, 
when drawn from the clean-oil storage chamber, the oil is 
ready for use again. The oil is pumped from the clean-oil 
storage chamber to a glass overflow tank where the amount of 
oil flowing can be observed. The overflow tank resembles 
somewhat a large sight-feed oil cup except that there is no 
sight feed. Three pipes enter the bottom of the overflow tank; 
one through which the clean oil is pumped into the tank, one 
through which the oil is distributed to the various bearings, 
and one through which the excess oil flows back to the clean- 
oil compartment in the filter tank. The end of the overflow 
pipe is placed so that the overflow tank is kept about half full 
of oil. The end of the inlet pipe is placed above the surface of 
the oil so that the operator can see that oil is being supplied. 
The pipe distributing oil to the bearings is placed at the bottom 
of the overflow tank so that, if necessary, all of the oil can be 
drawn off to the bearings. At the various bearings, the oil 
pipes are provided with one or more sight feeds, each of which 
has a needle valve with which to regulate the flow of oil. Oil¬ 
ing systems of this kind do not supply cylinder oil because but 
little of it can be returned for use the second time. Cylinders 
of large engines are therefore frequently oiled by such oilers 
as those shown in Figs. 6 and 7. 


AUTOMOBILE-ENGINE LUBRICATION 


CLASSIFICATION 

28. The many different systems by which the moving 
parts of automobile engines are supplied constantly with oil 
while the engine is at work can be broadly divided into splash 
lubrication systems, pressure-feed lubrication systems, and 
combined splash-and-pressure-feed lubrication systems. 




GAS-ENGINE LUBRICATION 


19 


29. In the splash lubrication system, the lower part of the 
crank-case contains lubricating oil into which the lower ends 
of the connecting-rods dip at every revolution, churning the oil 
into a dense mist and throwing it all over the internal surfaces 
of the engine. The two common forms of this system are the 
circulating constant-level splash system, and the non-circulating 
constant-level splash system. In the circulating constant-level 
splash system , the oil is transferred from a reservoir, in much 
larger quantities than is needed, into troughs placed beneath the 
connecting-rods, from which troughs the oil overflows back to 
the reservoir, whence it is sent back to the troughs again. The 
oil is thus continually circulated. In some circulating constant- 
level splash systems, individual troughs are used, one being 
placed under each connecting-rod; the oil reservoir is then in 
the bottom of the crank-case and is open at the top. In other 
systems, the oil reservoir, when in the bottom of the crank¬ 
case, is closed on top by a horizontal partition in which the 
troughs are formed, each trough having an overflow through 
which surplus oil flows back to the reservoir. 

The other class of splash lubrication system is spoken of as 
the non-circulating constant-level system. In this system, oil 
is taken from a reservoir by a pump and delivered, in the right 
quantity, to troughs into which the ends of the connecting-rods 
dip. The oil reservoir may form part of the crank-case or be 
entirely separate from it; the delivery of the pump is usually 
adjustable, and fresh oil is delivered to the splash troughs at 
all times, in which respect this system differs from the 
circulating system. 

The circulating constant-level splash system is in use in the 
great majority of four- and six-cylinder engines. The non¬ 
circulating constant-level splash system is little used at the 
present time, as the chief exponents of this system have now 
gone over to the manufacture of eight-cylinder engines, on 
which the use of the splash system is not practicable. 

30. In a pressure-feed lubrication system, as implied 
by the name, the oil is supplied to the rubbing surfaces under 
pressure. In the strictest sense, the oil would be supplied to 


20 


GAS-ENGINE LUBRICATION 


all rubbing surfaces under pressure; as carried out, however, 
oil under pressure is usually supplied only to the crank-shaft 
main bearings, crankpins, wristpins, and timing gearing. The 
oil thrown off from the crankpins is usually relied upon to 
lubricate the cam-shafts, cylinders, and other rubbing surfaces. 
Pressure-feed lubrication systems are divided into two classes, 
the low-pressure lubrication system, and the high-pressure 
lubrication system. 

In the low-pressure lubrication system, oil is raised either by 
a pump or other convenient means to an elevated position, 
whence it flows by gravity through individual tubes to the 
various bearings, and then drains to the bottom of the crank¬ 
case to be circulated again. 

In the high-pressure lubrication system, oil is taken from a 
reservoir, usually in the bottom of the crank-case, and delivered 
by a pump or pumps under pressure ranging from 3 to 
15 pounds per square inch to the various bearings; in racing 
cars much greater oil pressures are often used. In present-day 
practice, a single pump is employed, which discharges into a 
manifold from which branch pipes lead to the various bearings; 
individual pumps for each bearing have been employed, how¬ 
ever, in many cars. 

31. In combined splash-and-pressure feed lubrica¬ 
tion systems, many different combinations of the various 
forms of splash and pressure systems are possible and have 
been used. One form employs pressure feed to the main crank¬ 
shaft bearings, the overflow from these bearings flowing into 
troughs below the connecting-rods, from which the crankpins, 
wristpins, cylinders, etc. are lubricated by splash lubrication. 
In another system, oil is supplied only to the cylinders under 
pressure; all the bearings are lubricated by the splash system. 
Other combinations than those given here may be used. 


SPLASH LUBRICATION SYSTEMS 

32. A circulating constant-level splash system used in some 
engines is shown in Fig. 10. Other systems of this class differ 
in details of construction, but operate on the same general 




21 

























































































































































































































































































22 


GAS-ENGINE LUBRICATION 


principles. In this lubrication system, a gear-pump is em¬ 
ployed for circulating the oil, but other forms of pumps could 
be used, and are used in other engines. The oil reservoir a is 
formed in the lower crank-case and has fitted to it, at its rear 
end, the oil pump b. The oil in the reservoir flows to the oil 
pump through a screen c, whereby it is strained, and is pumped 
through a pipe (not shown) connected to the passage d of the 
oil pump to a sight feed and then flows through the pipe e, 
which is on the outside of the left side of the crank-case, and 
four nozzles f, to the four oil troughs g. These oil troughs are 
formed in a horizontal partition and are located directly 
beneath the connecting-rods. The oil in the troughs is kept at 
a constant level by the oil pump delivering a larger quantity 
than is needed; the excess oil overflows the troughs through 
the openings h and drains back into the reservoir a to be cir¬ 
culated again. The oil pump in this case is driven from the 
engine cam-shaft i by bevel gears. The driving shaft j of the 
oil pump is made in two parts that are connected by a helical 
spring k, which acts as a universal joint and hence takes care of 
any lack of alinement between the two parts of the shaft. The 
driving shaft is made in two parts to permit quick and easy 
removal of the oil pump. The timing gears are lubricated by 
splash from the crank-case. 

33. Non-circulating constant-level splash systems, as well 
as low-pressure systems, and combined splash and pressure- 
feed systems, have been largely superseded by the constant- 
level splash system, or the high-pressure system, and will there¬ 
fore not be described in detail herein. 


HIGH-PRESSURE LUBRICATION SYSTEMS 

34. Several American cars employ a pressure-feed oiling 
system in which the oil under quite a high pressure is delivered 
to the various crank-shaft bearings, and the oil thrown off of 
these bearings in the form of a fine mist is relied on to lubri¬ 
cate the cylinders and various parts of the engine. This sys¬ 
tem is used almost exclusively in the eight- and twelve-cylin- 



GAS-ENGINE LUBRICATION 


23 


der Y-type engines, because with such engines, broadly speak¬ 
ing, the cylinders could not be equally lubricated by an ordi¬ 



nary splash system. With such a system, the connecting- 
rod ends would throw practically all the oil from the splash 


Fig. 11 










































































































































































24 


GAS-ENGINE LUBRICATION 


troughs into the right-hand set of cylinders, the engine, as 
usual, running counter-clockwise when viewed from the 
driver’s seat. For this reason, the left-hand set of cylinders 
would be under-oiled, and the right-hand set over-oiled. 

35. A good example of a high-pressure lubrication system 
is shown in Fig. 11. The bottom of the lower crank-case 
forms an oil reservoir a, from which the oil is taken through 
a strainer by an oil pump b of the gear-type and discharged 
through the pipe c into a second oil strainer d, from which the 
oil passes through a pipe e into a distributing manifold /. This 
manifold, through distributing pipes, is connected to the for¬ 
ward bearing g, the middle bearing h, and the rear bearing i 
of the crank-shaft, which in the engine shown has seven main 
bearings. A pipe j leads from the manifold f to the timing 
gears k, and a pipe / leads to a pressure gauge m placed on the 
dashboard. The crank-shaft is drilled with radial holes n 
and axial holes o through the various journals; holes p in the 
crank-webs connect the axial holes o. From each crankpin end 
of the connecting-rods an oil tube q leads to the piston pins r. 
The excess oil drains back to the oil reservoir and is pumped 
back to the oil-distributing system. The oil reservoir is sup¬ 
posed to be kept filled to the level of the test cock s; it is filled 
through the funnel t and drained through the drain cock u. 

36. In most pressure-feed lubrication systems of the high- 
pressure type and using a single pump, a relief valve is fitted; 
this valve can be adjusted by hand to any pressure that will 
produce satisfactory lubrication. Thus, if the engine smokes 
continually it is getting too much oil; the obvious remedy is to 
reduce the pressure in the oiling system until smoking ceases, 
which is done by adjusting the relief valve to open at a lower 
pressure. The relief valve acts by discharging some oil from 
the delivery side of the oil pump back to the suction side. In 
high-pressure lubrication systems in which an individual pump 
is used for each oil pipe, no relief valve is needed, as the 
delivery of each pump is made adjustable; this system is now 
quite rare in American practice. 


GAS-ENGINE LUBRICATION 


25 


CYLINDER LUBRICATORS 

37. When the oil is fed directly to the surface of the 
piston through the cylinder wall, the piston must be a little 
longer than the stroke, so that some portion of the piston will 
always be over the opening through which the oil enters; other¬ 
wise, the front or the back end of the piston will scrape the 
oil away, instead of working it between the piston and the 
cylinder wall. As the single-acting gas-engine piston serves 
also as a crosshead, it is always so long that this requirement is 
met. Oil is fed to the cylinders 
of horizontal stationary engines 
either from sight-feed oil cups 
or from some form of mechan¬ 
ical lubricator that delivers a 
fixed quantity of oil per revolu¬ 
tion. 


38. Sight - Feed Lubri¬ 
cator. — When a sight-feed 
oiler is used,, cylinder, piston, 
and piston pin may all receive 
their lubricating oil from the 
same adjustable sight-feed oiler, 
as shown in Fig. 12. After the 
glass cup has been filled, the 
supply is regulated by the valve 
stem a, so that about five to ten 
drops of oil are fed per minute. 

When the proper adjustment is 
obtained, the valve is locked by 
the jam nut b. In order to turn on or shut off the oil feed, the 
arm c is turned to one side, which can be done without dis¬ 
turbing the adjustment of the quantity of oil supplied to the 
piston. The sight glass d permits the operator to see whether 
or not the oiler is working properly. The oil passes through 
the hole e to the piston f, and is distributed over the surface by 
suitably cut oil grooves. 



Fig. 12 












26 


GAS-ENGINE LUBRICATION 


39. The piston pin is surrounded by the bronze bushing g. 
Fig. 12, and the wear is taken up by the screw h. Oil is supplied 
from the oiler to the piston pin through the tube i when it 
registers with the hole e, or by hand when it registers with 
the hole j in the cylinder wall. The oil tube k, in the con¬ 
necting-rod head, receives the oil from the tube i in the piston, 
being directly below it. In order to be sure that the piston pin 
is well oiled from the start, the crank-shaft is turned until the 
piston has reached its outer dead center, when the tube i will 
register with the oil hole j in the cylinder wall and the oil tube k 
in the connecting-rod head. Oil can then be supplied by a 
hand oiler direct to the piston pin. While the engine is run¬ 
ning, some of the oil supplied to the piston finds its way 
through the tube i, whence it is conveyed either direct to the 
tube k or to the countersink in the connecting-rod head, which 
communicates with the hole in the tube k through small holes 
drilled horizontally into the wall of the tube on a level with the 
bottom of the countersink. 

40. Pump Lubricator. —Ordinary cylinder oil tends to 
grow thick in cold weather, and to avoid this disturbing 
influence on the rate of feed, mechanical oilers are often used, 
which have, instead of the arrangement just described, one or 
more positive pressure pumps that deliver a definite quantity 
of oil for each revolution. In the most approved form, these 
lubricators have one small pump for each cylinder supplied, 
and often have other pumps to feed the main bearings. The 
stroke of the pump may be adjusted according to the sort of 
oil used. Some device of this sort is always necessary for 
engines working under extreme variations of speed, since any 
other method of feeding the oil would give too much or too 
little, according to whether the engine was running slow or fast. 

41. Splash Lubricator. —In many vertical engines, the 
oil is not fed to the piston directly as described, but is splashed 
to it by the cranks. This arrangement has the advantage that 
the same splash of oil may be made to lubricate practically all 
other parts of the motor, including the crank-shaft bearings, 
over which pockets may be cast in the crank-case to catch the 


GAS-ENGINE LUBRICATION 


27 


oil. W hen the splash system of lubrication is used, the oil may 
be delivered to the crank-case by an automatic pump, but it is 
more common to feed it periodically by hand. In stationary 
engines, a gauge is often attached to the outside of the crank¬ 
case, which shows the level of the oil within. In these engines, 
the crank-case is large enough to hold oil sufficient for several 
days’ service. 

Splash lubrication is used only on vertical engines, because 
In horizontal engines it would be impossible to prevent an 
excessive quantity of oil from being carried into the cylinder, 
where it would cause smoke in the exhaust and cover the 
igniter with soot and clog the valves. 


BEARINGS 


SHAFT BEARINGS 


GENERAL, CONSIDERATIONS 

42. Definitions. —When it is the regular duty of a 
machine part to rotate, as when an axle or a shaft turns, it 
must be restrained or held at a definite place by a suitable 
support. A portion of the rotating part is in direct contact 
with the support that holds it and to which it fits. This con¬ 
tact portion of the rotating part is called the journal, and the 
part that surrounds and carries the journal is called the 
Bearing:. 

When the bearing is made separate, it is called a bushing:, 
or sleeve, if in one piece, and a box, if in two or more pieces. 
The term bearing is sometimes used, rather loosely, to mean 
both the journal and the bearing proper; the distinction made 
here, however, has the support of the best authorities. 

43. Metals for Bearing:s. —Journals are commonly 
made of either iron or steel, while bearings are generally made 
of a softer metal. This is done for two reasons. There is less 
friction between a journal of hard metal and a soft-metal 

356-5 






28 


GAS-ENGINE LUBRICATION 


bearing than between two hard metals, and it is cheaper to 
repair or replace a worn bearing than a worn journal. The 
principal bearing metals are brass, bronze, and Babbitt metal, 
commonly called babbitt. Brass is an alloy of copper and zinc; 
it varies in color from a bright yellow to a dark copper color. 
Some brasses are quite soft, while others are too hard for use 
as bearings. Bronze is an alloy of copper and tin, though lead 
is also added, at times. 

Since brass and bronze are so extensively used for bearings, 
it has become common practice to call the two parts of an 
ordinary brass or bronze bearing the brasses. 

44. Babbitt is much softer than either brass or bronze. 
Its low melting point is an element of safety because the babbitt 
will melt and run out of the bearing before a temperature high 
enough to make the bearing seize and damage the journal has 
been reached. There are in general three kinds of babbitt. 
Tin babbitt is an alio yin which tin is the chief metal. This is 
frequently called genuine babbitt , though that must not be 
understood to mean that tin babbitt is necessarily any better 
than other babbitts. In fact there are certain uses for which it 
is not so well suited as are some of the other babbitts. Tin 
babbitt, as a rule, melts at a lower temperature than the other 
babbitts and it is very fluid when melted. Bearings lined with 
this metal may therefore have a thin lining. 

Zinc babbitts contain so much zinc that its properties are 
more evident than are those of tin. Zinc babbitt melts at high 
temperature and is not very fluid when melted. Bearing linings 
made of this metal must therefore be rather thick which some¬ 
times makes the bearings look rather cumbersome. This 
babbitt is tough and wears well. 

Lead babbitt is composed of lead alloyed with small amounts 
of other metals to give certain desirable qualities. Lead 
babbitt is largely used because it is cheap. When a suitable 
grade of lead babbitt is used, it will be found to have satisfac¬ 
tory toughness and wearing qualities. Lead babbitts are of 
four grades, known respectively as Nos. 1, 2, 3, and 4, of 
which No. 1 is the hardest.and No. 4 is the softest. 


GAS-ENGINE LUBRICATION 


29 



45. Phosphor-bronze, made according to the specifica¬ 
tions of the Society of Automobile Engineers, is an alloy con¬ 
taining approximately 80 per cent, 
of copper, 10 per cent, of lead, 

10 per cent, of tin, and a quantity 
of phosphorus not exceeding one- 
quarter of 1 per cent., nor less than 
five one-hundredths of 1 per cent. 

This bearing metal stands up well Fig - 13 

under heavy loads and lasts well even under scanty lubrication. 

In automobile engines, it is used for both cam¬ 
shaft and wrist-pin bearings and in other places 
where it may be in contact with a hardened-steel 
journal. The use of phosphor-bronze boxes in 
connection with soft-steel journals is inadvis¬ 
able, owing to the rapid wear of the soft steel, 
even under ample lubrication, when this com¬ 
bination of box and journal exists. 

4G. White brass is an alloy that contains 
from 3 to 6 per cent, of copper, not less than 
65 per cent, of tin, and from 28 to 30 per cent, 
of zinc. This alloy is often used for main 
crank-shaft bearings and for connecting-rod 
crankpin bearings, giving excellent results in conjunction with 
soft-steel journals when generously 
lubricated at all times. 

47. Very excellent bearings are 
sometimes made by putting babbitt 
inserts over the inside surface of a 
brass box, as shown at a, in Fig. 13. 

Holes are drilled nearly through 
the brass and sometimes they are 
threaded roughly to give the babbitt 
plugs a hold, the threads being battered to keep the plugs from 
working loose. 

The bearing shown in Fig. 14 also has babbitt inserts. In 
this bearing, the babbitt is held in dovetailed slots a which 



Fig. 14 



Fig. IS 









30 


GAS-ENGINE LUBRICATION 


sometimes run spirally around the bearing. Some bearings 
have full babbitt linings as shown in Fig. 15 at a. Sometimes 
the babbitt lining is cast in the bearing and at other times it is 
cast separately and fastened in the bearing with screws. When 
the lining is cast in the bearing, the lining must be fastened to 
the bearing. This may be done by drilling holes at intervals 
in the bearing, as shown in Fig. 13, and threading the holes to 
give the babbitt a hold, or by making one or more dovetailed 
slots in the bearing. 


OIL GROOVES IX BEARINGS 

48. Form and Arrangement of Grooves. —To insure 
uniform distribution of the lubricant over the bearing surface, 
it is common practice to cut oil grooves in the surface, espe¬ 
cially when the bearing is to sustain heavy pressures. In a 
long bearing, a shallow straight groove is cut extending each 
way from the oil hole or holes to within inch of each end of 
the bearing cap. In some bearings the grooves are arranged in 
H shape, in others in X shape as at b in Figs. 14 and 15, and 
sometimes in V shape. They are semicircular in cross-section, 
and the oil or grease flows toward the outer ends, lubricating 
the journal. 

In stationary gas engines, it is good practice to provide 
grooves in bearings that are 6 inches long or over. In bearings 
less than 6 inches long provided with a single oil hole, the 
chamfering of the edges where the two parts of the bearing 
come together is depended on to distribute the oil, and no oil 
grooves are required. 

49. Lubrication of Plain Bearings.— The lubricant is 
supplied to the bearing in a liquid form, and it flows through 
channels provided for it. Grease is rather plastic, especially 
when cold, and needs to be forced into the bearing. This is 
done by the use of an automatic grease cup having a 
spring-loaded piston, attached to the cover, that forces the 
grease down. When the bearing becomes warm, the grease 
becomes more fluid, and flows to the rubbing surfaces more 
rapidly. 



GAS-ENGINE LUBRICATION 


31 


50. Oil should always be fed to a bearing on the unloaded 
side, and the oil grooves in a bearing should be on that side. It 
is a somewhat common but poor practice to cut oil grooves in 
the loaded side of a bearing. The effect of this arrangement is 
that the oil is squeezed out from the bearing under the load. 
If the oil is supplied in abundance to the unloaded side of the 
bearing, it will be carried around by the turning of the shaft. 
In oiling systems in which the oil is fed rapidly to a bearing, 
and is collected and used over again after it works out, the 
best plan is not to extend the oil grooves the length of the 
bearing, as is often done, but to limit the grooves to about one- 
half of the length of the bearing 
and locate them as near the middle 
as possible. This will cause the 
oil to flush the bearing continually 
as it works out at the ends, there¬ 
by carrying with it the metal worn 
from the bearing surfaces. 

51. It is particularly common 
to find the crankpin brasses 
grooved on the pressure side as 
well as on the cap side, the reason 
generally being that, when the 
splash system is used the oil is in¬ 
troduced on this side. If trouble 
is experienced with crankpin 
bearings arranged in this manner, in a vertical motor with 
splash lubrication, it will be well to fill up the grooves in the 
pressure brass with solder, and supply the oil wholly through 
the bottom brass. To do this, a hole should be drilled and 
tapped in the cap for a piece of brass tubing T 5 ¥ inch outside 
diameter, as shown in Fig. 16. The tube a should be bent so 
that, when it dips into the oil on the bottom swing of 
the crank, it will act as a scoop, and the lower end of it is 
preferably beveled off as the sketch indicates, so as to give an 
elongated opening. The tube is firmly fastened in the cap b , 
and the brass c has an oil hole d about inch in diameter 




















32 


GAS-ENGINE LUBRICATION 


drilled through it, connecting with a deep, cross-shaped 
groove e. On the bottom swing, the oil will be scooped up into 
the groove, which will retain enough of it during the remainder 
of the revolution to lubricate the bearing. Another arrange¬ 
ment is to cut a square hole through the cap brass, and fill it 
with a felt pad a little thicker than the brass itself, so that it 
will be under slight compression. This pad will absorb the oil 
and transmit it to the bearing. Unless provision is made by one 
of these methods for retaining the oil as it comes up, it is likely 
to be thrown out by centrifugal force. Practically all modern 
automobile engines depending on the splash system for their 
lubrication, have a small projection made on the large end of 
the connecting-rod to assist in the lubrication of the connecting- 
rod bearing, and also to increase the force of the splash. 


TYPES OF BEARINGS 


52. Classification of Main Bearings. —The oldest 
and simplest form of bearing used in gas-engine practice is the 
plain bearing, in which the journal of the shaft fits in a 
sleeve called the bearing, or box, and touches the supporting 



Fig. 17 


surface along its entire length. A type closely related to the 
plain bearing is the ring-oiled bearing, in which oil is carried 
to the journal by means of a ring, as already described. In 
roller bearings, rollers are interposed between the bearing 
and the journal, thus reducing the bearing surface and having 



















GAS-ENGINE LUBRICATION 


33 


rolling instead of sliding friction. In ball bearings, a num¬ 
ber of balls surround the journal and lie between it and the 
bearing proper. Each ball thus touches the journal and the 
bearing surface in single points, instead of along lines. There 
is rolling friction, however, and the frictional resistance is 
much less than in ordinary bearings. 

53. Plain Bearing.— The earliest bearings were of the 
plain type, and probably more bearings of this type are used 
than of any other. A plain bearing is shown in Fig. 17, which 
in (a) shows a section through the axis of the journal, and in 
( b ) an end view. The journal is shown at a and the brasses 


X 



at b and c. The bearing is divided into two parts, the lower, 
which shows a part of the frame or pedestal d, and the upper 
part e, known as the cap. A plain bearing will give excellent 
results when well made and properly fitted. When worn, new 
brasses can be fitted and the bearing will be as good as when 
new. The brasses of a plain bearing may be provided with 
babbitt inserts or linings as shown in Figs. 13, 14, and 15. 
Plain bearings are usually lubricated by allowing oil to flow 
between the rubbing surfaces by gravity from an oil cup. 

54. End-Plate Main Bearing. —In Fig. 18 is shown a 
plain main bearing as used in a vertical engine. The box is 























34 


GAS-ENGINE LUBRICATION 


made in two parts, of brass or bronze, and is lined with babbitt. 
The end plate a is circular and turned to fit the opening in the 
crank-case, to which it is bolted. The upper brass b is held in 
a central position on the shaft by two capscrews. There is 
little or no pressure on this brass, hence it does not wear; its 
duty is to prevent the shaft from lifting off the lower bearing 
and to aid in the distribution of the oil. The lower brass c is 
held in position by the weight of the shaft and the wedges d 
and e, which also serve to adjust the brass to the shaft so as to 
give as even a bearing between the shaft and the lower brass as 
possible. The screws on either side of each wedge are for the 
purpose of moving the wedges laterally to adjust the brass and 

also to hold the wedges in 
position when once prop¬ 
erly adjusted. The cham¬ 
ber / below the bearing 
catches the surplus oil, and 
the hole g permits it to flow 
to the crank-case. Any sur¬ 
plus oil in the crank-case is 
drained off to a purifier or 
filter. 

The adjustment of the 
tower brass permits the 
alinement of the shaft to be 
maintained. Any wear of 
the journal or bearing can be easily and quickly taken up by 
changing the position of the wedges. The bearing is oiled by 
means of the sight-feed lubricator shown at h. 

55. Ring-Oiled Bearing. — A ring-oiled bearing is 
shown in Fig. 19, with the journal at a and the brass sleeve at b. 
An important part of this bearing is the oil reservoir c below 
the bearing, and the ring d that rests on the journal and extends 
down into the oil. The ring is narrow and light, and when the 
engine is running, the upper part of the ring moves , with the 
shaft; so that the lower part picks up the oil and raises it to 
the top of the shaft. By this means, a good supply of oil is 
































GAS-ENGINE LUBRICATION 


35 


continually brought to the journal, keeping it well lubricated. 
Light chains are sometimes used for such work, instead of 
rings, and they have the advantage that they may be put in 
place when the shaft is in the bearing. 

5G. Holler Bearings.—There are three types of rollers 
used in roller bearings, the plain cylindrical, the spiral, and the 
conical. The plain cylindrical roller bearing consists of a 
set of cylindrical rollers between the journal and a casing, or 
between a sleeve and a casing, as shown in Fig. 20. This bear¬ 
ing is made up of a cage a, with rollers b extending nearly the 
whole length, a casing d outside the rollers, and a sleeve e 
inside. The cage simply holds the rollers, and does not come 
in contact with the sleeve e. The ends of the rollers are pro- 



Fig. 20 


vided with balls c, which reduce the friction and wear, and 
keep the rollers in true alinement with the shaft. This pre¬ 
vents all twisting of the bearing, and makes it more reliable and 
satisfactory. 

The roller bearing will not sustain as much of a load for the 
same size of journal as will the plain bearing. It will, however, 
reduce the friction for light or moderate loads when running at 
moderate speed. The plain rollers for bearings are made either 
hollow or solid, with the ends hollowed out for the supports 
that hold them in place. Solid rollers are cheaply made, and 
will sustain more weight than hollow rollers of the same size. 

57. A spiral roller bearing is shown disassembled in 
Fig. 21. The rollers a are wound helically from flat steel and 




















36 


GAS-ENGINE LUBRICATION 


are ground cylindrical after hardening. They are set in a 
cage b made of two washers properly spaced by ribs c, to which 
the washers are securely riveted. Projections d on each washer 
enter the ends of the rollers and thus prevent them from falling 
out of the cage. The rollers are sometimes run directly on the 
journal and the box of the bearing; in better work, both the 
journal and the box are protected by removable liners. A liner 
for the journal is shown at e, and a liner for the box at /. 
These liners are formed from soft sheet steel, and since they 
are split as shown, they are easily forced into place or removed 
when worn enough to need replacement. The outer liner 
should be held from turning in the box by making the conical 
projection g enter a hole drilled for this purpose into the box. 



A liner for the journal is often omitted; when the metal of the 
journal is very soft, however, a case-hardened steel liner is 
necessary. This liner may have the form shown at e or it may 
be in the form of a solid bushing that is pressed on the journal. 
Likewise, the outer liner may be in the form of a solid bushing. 

58. The rear axle of an automobile, shown in Fig. 22, 
illustrates the use of roller bearings in practice. In the small 
view (a) is shown the external appearance of the axle and in 
( b ) the interior construction. The two views are not shown to 
the same scale but when a part appears in the two views, the 
same reference letter is given. The housing a encloses the 
whole axle, keeps the dust out and holds a quantity of oil or 





































37 


Fig. 22 


























































































































38 


GAS-ENGINE LUBRICATION 


grease for purposes of lubrication. The axle shaft is in two 
parts b and V each of which is supported in two roller bear¬ 
ings c and d. Power is transmitted to the axle through the 
propeller shaft e, which runs in a roller bearing f, and drives 
the differential gears g. There is a thrust that tends to force 
the propeller shaft and each part of the axle shaft away from 
the differential. This thrust is counteracted by three thrust 
bearings h, i, and /. The bearing at h is a ball thrust bearing 
but the bearings at i and j are plain babbitt rings. The axle 
housing is kept partly filled with grease in which the gears run 
and which works out to the other bearings. The bearing d at 
the end of the axle does not always receive sufficient lubrication 
from this source and a small grease cup, not shown, which 
makes up the deficiency, is put on each end of the axle. 

59. A conical-roller bearing:, as implied by the name, 
employs conical, or tapered, rollers, that is, rollers that are 
frustums of cones, running in contact with tapered inner and 
outer races. A bearing of this form, widely used in automo¬ 
bile work, is shown in Fig. 23. In ( a ) is shown a section 
through the inner and outer race with a roller a between the 
conical (tapered) surfaces of the inner race b and the outer 
race c. The inner race is cylindrical on its inside, and the outer 
race on its outside. The inner race has two ribs with conical 
sides, the rib d entering a corresponding groove e in the small 
end of the roller a. The conical face of the rib / bears against 
the conical large end of the roller, as shown. The ribs d and f, 
in conjunction with a cage in which the rollers are set, hold the 
rollers in proper alinement with the races. The cage is shown 
separately in (b) ; it is pressed in one piece from sheet steel 
into the form shown. The inner race is shown in perspective in 
view (c), and assembled with the cage and rollers, in ( d ). 
When thus assembled, the inner race, cage, and rollers cannot 
separate. The outer race is shown separately in ( e ), and the 
whole bearing assembled in (/). 

The outer and inner races have their bearing surfaces 
formed as frustums of cones whose apexes coincide and lie on 
the center line of the journal; the center lines of the rollers lie 


GAS-ENGINE LUBRICATION 


39 


on the surface of a cone whose apex coincides with that of the 
inner and outer races, and consequently the rollers have a true 



rolling motion. As in cylindrical roller bearings, the cage for 
the rollers prevents their sidewise displacement. 












































40 


GAS-ENGINE LUBRICATION 


A tapered roller bearing carries radial and axial loads., and 
any radial looseness due to wear is readily taken up by forcing 
the inner race farther into the outer race. This form of bear¬ 
ing is always mounted so as to permit this operation to be 
easily done. The races and rollers are made of hardened steel 
and are very accurately ground after hardening. Tapered 
roller bearings are largely used in the construction of rear 
axles. 


GO. The use of the conical-roller bearing in the rear axie 
construction of an automobile is shown in Fig. 24. The axle 
shaft a is made in two parts, as is the common custom, and 
the two outer ends of the axle shafts are supported by the roller 
bearings b placed on the inside of the ends of the rear axle 
housing c. The whole differential d, including the driving 
gear e riveted to the differential housing f, instead of being 
carried by the axle shaft is supported by its own bearings g, 
one on each side, the bearings being placed in this case in the 
removable differential carrier h, which is bolted to the rear- 
axle housing. The inner ends of the halves of the axle shaft 
are spline d, that is, have a number of rectangular key ways cut 
into them, and enter the correspondingly splined hubs of the 
differential side gears i, which drive the halves of the axle 
shaft. While the inner axle-shaft ends are splined in this case, 
some manufacturers use squared ends entering squared holes 
of the differential side-gear hubs, but in neither case are the 
inner axle ends rigidly fastened to the differential side gears as 
is the case with the plain live axle. The bevel driving pinion j 
tends to thrust the whole differential to the left; this thrust is 
resisted by the left bearing g, which being a tapered roller 
bearing is adapted in itself for carrying thrust loads. 

61. Ball Bearings.—A ball bearing consists of at least 
three elements, an inner casing, known as the inner race, an 
outer casing, known as the outer race, and one or more rows of 
balls. The inner race is attached to the shaft, and forms the 
journal; the outer race is attached to the bearing housing, and 
serves as a box; the balls provide for the rolling friction. 







sS^\\Vn 


XXWXXXXX" 


4J 

I 


Fig. 24 








































































































































































42 


GAS-ENGINE LUBRICATION 


62. A typical ball bearing is shown in Fig. 25 (a), in which 
illustration part of the outer race a is cut away in order to show 

the assembly. The outer race 
a and the inner race b are 
grooved to a larger radius 
than that of the balls c in 
order that the balls may be in 
contact with each race at a 
single point in the same plane 
as the centers of the balls. 
The balls are introduced be¬ 
tween the races through a slot 
in the outer race, which slot cannot be seen in view (a), but is 
indicated at d in the cross-section shown in ( b ). 



Fig. 25 


TAKING UP WEAR IN BEARINGS 

63. Some forms of connecting-rods are provided with 
means of taking up wear on the bearings by the use of shims, 
or thin strips of copper or brass, which are interposed between 
the large end of the connecting-rod and the bearing cap. The 
cap is bolted down tight against these shims, and when the 
bearing becomes worn one or more shims are taken out on each 
side. Provided that the bearing has not been cut and is not 
badly worn out of shape, this will take up the wear satisfac¬ 
torily. Care must be taken to remove shims of the same num¬ 
ber or thickness from each side of the bearing. After the bolts 
are tightened there must be not the slightest evidence of tight-, 
ness or binding in the bearings; for if there is, the oil will 
squeeze out and the bearing will begin to overheat and cut. 

If the crankpin bearing is not provided with shims, it becomes 
necessary to file the flat face of the cap where it abuts against 
the large end of the rod, in order to close up the bearing. This 
must be done with great care, in order to avoid taking off more 
metal at one end of the bearing than at the other, which would 
cause it to be tight at that end. The work should be done 
slowly, the cap replaced frequently, and the tightness of the 
bearing tried. 









GAS-ENGINE LUBRICATION 


43 


If the bearing is already cut, or if it is worn badly out of 
shape, so that the connecting-rod will rock sidewise when the 
brasses are brought together as close as they will come without 
binding, it is necessary to scrape the bearing to a fit. 

64. The scraping- of a bearing, whether a crankpin 
bearing or a main bearing, is done with tools called scrapers, 
two of which are shown in Fig. 26. Old three-cornered or 
half-round files, with the teeth ground off and the edges 
worked down smooth on an oilstone, make very good scrapers. 
When a bearing has been scraped approximately true, the 
crankpin should be rubbed lightly with red lead or graphite 
mixed with oil, and the bearing replaced. The shaft should 
then be revolved a couple of times, and when the bearing is 



taken apart again the high spots on the brasses will be indicated 
by the red lead on them. These should be scraped down, the 
brasses again fitted on the pin, and the operation repeated until 
the brasses bear evenly on the journal. 

It is very essential that the bearing be scraped true, so that 
the connecting-rod will be perfectly square with the shaft. 
Unless this is done, the pressure will come at one end of the 
bearing, which is likely to be speedily ruined. For this reason, 
the novice should not undertake the work, but should employ 
an experienced machinist, or send the engine to a repair shop. 

65. Frequently, the meeting edges of the crankpin brasses 
are beveled, as shown at a, Fig. 27. This is done to prevent 
possible binding of these edges, which receive little, if any, of 
the pressure on the piston. It is better, however, not to extend 

356—6 




44 


GAS-ENGINE LUBRICATION 


the bevel out to the ends of the bearing, as that permits the oil 
accumulating in the grooves formed by the bevels to escape 
instead of being carried around the pin. 

It will sometimes be found that the crankpin itself has been 
worn out of round, being flattened on one side. When this is 
the case, it is useless to take up the lost motion in the bearing 
before the crankpin itself has been trued up. 

66. Adjustment of Bearings. —It is sometimes thought 
unwise to make bearings adjustable because it gives an opportu¬ 
nity for inexperienced men to do damage through lack of 
judgment. One of the principal causes of hot bearings is 
setting up the brasses too tightly. Sometimes as soon as a 

pound or noise about an 
engine is heard, the man in 
charge concludes that a bear¬ 
ing is slack and proceeds to 
tighten it. There are num¬ 
erous other causes of pound¬ 
ing in engines besides slack 
bearings, and the engineer 
should be fully convinced 
that the pound is caused by 
slack brasses before setting 
them up. Bearings on an 
engine that is in line and in good order, if properly adjusted, 
will run smoothly and noiselessly for months without further 
adjustment, and it should be the object of an engineer to get his 
engine into that condition as soon as possible and to keep it so. 



HOT BEARINGS 

67. Observation of Bearings. —Bearings, particularly 
those of large engines, require constant watching. The engineer 
or oiler should know at all times the condition of every bear¬ 
ing and oil cup; this will make it necessary that the oil cups be 
examined frequently, to ascertain if they are feeding and if 
they contain sufficient oil, and that the oil in the cups be 
















GAS-ENGINE LUBRICATION 


45 


replenished whenever necessary. While making his rounds the 
engineer should feel with the palm of his hand the brasses of 
those bearings that have shown a tendency to heat and those 
that are most liable to heat. 


GENERAL, TREATMENT OF HOT BEARINGS 

08. Treatment When Bearing Begins to Heat. 
Should the temperature of any bearing rise much above the 
temperature of the surrounding atmosphere, the oil feed should 
immediately be increased; if the oil does not feed freely, the 
oil tubes should be opened by running a wire through them. 
If the bearing continues to get hotter, it may indicate that the 
brasses have been expanded by the heat and are therefore 
gripping the journal harder and harder the hotter they get. 
Sometimes the trouble may be avoided before the temperature 
has risen very high by loosening the bearing by backing off the 
capscrews a little and then supplying oil liberally. 

69. Dangerous Heating.— Should a bearing become so 
hot as to scorch the hand or burn the oil, there is immediate 
danger that the brasses will be damaged beyond repair and 
deep grooves be cut in the journals; if the brasses are bab¬ 
bitted, the soft metal will soon melt out and the engine will be 
disabled until new brasses can be substituted or the old ones 
rebabbitted. 

70. Remedies for Increased Heating.— If the means 
just described fail to reduce the temperature of the bearing, 
the engine should be relieved of its load and slowed down as 
much as possible, the cap nuts or key of the hot bearing should 
be slacked back, and the engine be allowed to run slowly until 
the bearing has cooled off. The engine should not, however, 
be allowed to stop while the bearing is excessively hot or the 
bearing will seize so that the engine cannot be started until the 
bearing is refitted. 

If necessary, the cooling may be hastened by pouring cold 
water upon the bearing, though this is objectionable, as it may 
cause the brasses to warp or crack by unequal contraction. 



46 


GAS-ENGINE LUBRICATION 


Putting water on a very hot bearing should be resorted to only 
in an emergency, that is, when an engine must be kept running 
regardless of a spoiled pair of brasses. Water may be used on 
a moderately hot bearing without doing very much harm. 

If the engine is not started again until the faulty bearing 
has become perfectly cool, the cap nuts or key should be set 
up a little before starting; otherwise, the brasses that have 
been slacked off may be too loose, and excessive thumping and 
pounding will result. 

71. Keeping; Engine With Hot Bearing; Running. 

If it is absolutely necessary in an emergency to keep the 
engine running under load while a bearing is very hot, the 
engineer must exercise his best judgment as to how he shall 
proceed. After slacking off the brasses, about the best he can 
do is to flood the inside of the bearing with a mixture of oil and 
graphite, sulphur, soapstone, etc., and the outside with cold 
water from buckets, sprinklers, or hose, taking the chances of 
ruining the brasses and cutting the journal. Of course, the 
engine must be stopped as soon as the emergency has passed, 
and the journal then stripped. It is to be expected that the 
journal will be found to be deeply grooved and the brasses cut 
and warped. If the brasses are babbitted, most of the babbitt 
will have melted out. But if the brasses are made solid, they 
can be refitted for at least temporary use or until new ones can 
be procured. 

72. Refitting a Cut Bearing. — The wearing surfaces 
of the brasses and journal must be smoothed off as well as 
circumstances will permit; but if the grooves are very deeply 
cut, it will be useless to attempt to work them out entirely, 
and if the brasses are very much warped or badly cracked, it 
will be best to put in new ones if any are on hand. If not, the 
old ones must be refitted and used until a new set can be pro¬ 
cured, which should be done as soon as possible. As for the 
journal, temporary repairs can be made by smoothing it with 
fine emery cloth, but at the first opportunity the journal should 
be trued up in a machine shop and the brasses properly refitted 
or replaced with new ones. 


GAS-ENGINE LUBRICATION 


47 


After a bearing has once been heated sufficiently to cut the 
brasses and journal or to warp or crack the brasses, it is after¬ 
wards constantly in danger of heating again, and the engine is 
thereby rendered unreliable. 


CAUSES AND PREVENTION OF HOT BEARINGS 


73. Causes. —The methods of prevention or cure of hot 
bearings will now be described in detail. Hot bearings are 
produced by the following causes: 


Brasses newly fitted 
Brasses refitted 
Brasses imperfectly fitted 
Brasses bearing unevenly 
Engine out of line 
Springing of bedplate 
Springing or shifting of outboard 
bearing 

Brasses too long 
Brasses pinching at edges 
Brasses set up too tightly 
Brasses too loose 


Brasses or journal cut 
Brasses warped and cracked 
Cut brasses and journals 
Oil feed stopped 
Oil feed insufficient 
Oil unsuited 

Oil dirty or of poor quality 
Grit in bearing 
Premature ignition 
Journal too small 
Engine overloaded 
External heat 


74. Brasses Newly Fitted. —The bearings of new 
engines are particularly liable to heat, due to the wearing sur¬ 
faces of the brasses and journals not having reached a perfect 
fit; therefore, if a new engine or one with new brasses is run 
at moderate speed and under light load, with rather loose 
brasses, until the journals and bearings adapt themselves to 
each other, there will be little danger of the bearings heating 
thereafter, if proper attention is given to their adjustment and 
lubrication. 


75. Brasses Refitted. —The bearings of an engine that 
has just been thoroughly overhauled and the journals and 
brasses of which have been refitted are liable co heat. The 
wearing surfaces of the brasses having been newly worked or 
machined, the surface of the metal is not smooth, and the 
brasses have not yet had a chance to adjust themselves to the 
journal. The engine, therefore, is in about the same condition 
as a new engine, so far as the bearings are concerned, and 



48 


GAS-ENGINE LUBRICATION 


should be treated in the same manner; that is, it should be run 
moderately until the brasses have accommodated themselves to 
the journal. 

76. Brasses Imperfectly Fitted. —Faulty workman¬ 
ship is a common cause of the heating of a bearing. The 
brasses in that case do not bear fairly or set squarely in their 
beds, and while they appear right to the eye, they may not be 
square in the bearing. A crankpin brass must set squarely on 
the end of the connecting-rod and the rod itself must be square. 
If the key, when driven, forces the brasses to one side or the 
other and twists the strap on the rod, the brasses will not set 
squarely on the pin and will bear harder on one side than on 
the other. The same is true of the shaft bearings. If the 
brasses do not bed fairly on the bottom of the casting or do not 
go down evenly, without springing in any way, they will not 
run as they should, and heating will result. Continual heating 
of bearings is almost always caused by badly fitting brasses. 
This is a defect that should be looked for and, if found to 
exist, should be remedied at once. 

In many cases, trouble with connecting-rod bearings can be 
traced to crankpins that are not perfectly round. With crank- 
pins from .003 inch to .005 inch out of round, it would become 
absolutely impossible to keep the bearings in good working 
order. 


77. Brasses Bearing- Unevenly.— In order that a bear¬ 
ing may run freely, there must be a little play between the 
brasses and their beds; this permits a slight movement of 
the brasses when pressure is exerted on them by the shaft; 
and notwithstanding the fact that they may have been most 
carefully fitted in the shop, they must be run a certain amount 
in order to adjust themselves properly. This is especially the 
case with the bearings of large engines, and the same condi¬ 
tions will obtain every time the brasses are removed. It seems 
almost impossible in practice to put the brasses of a large bear¬ 
ing back again just where they were before removal; it always 
requires time for them to settle into their old places; therefore, 
they should not be disturbed unless there is a positive necessity 


GAS-ENGINE LUBRICATION 


49 


for doing so. The direct cause of the tendency to heat in this 
instance is that the brasses do not bear evenly on the journal 
after the several parts of the bearing are assembled. 

78. Engine Out cf Line.— If an engine is not well 
lined—that is, if the bearings are not lined up properly—the 
brasses do not bear fairly upon the journals. This will reduce 
the area of the wearing surfaces in contact to such an extent 
that the friction is in excess of the practical limit, and will 
necessarily cause heating. 

If the engine is not greatly out of line, the working condition 
may be considerably improved by refitting the brasses by filing 
and scraping down the parts that bear most heavily on the 
journal. 

The crosshead guides of an engine out of line are liable to 
heat, and they will continue to give trouble until the defect is 
remedied. The guides may also heat from other causes; for 
instance, the gibs may be set up too tightly. Of course, if such 
is the case, they should be slacked off. The danger of the 
guides heating may be very much lessened by chipping zigzag 
oil grooves in their wearing surfaces and by attaching' to the 
crosshead, oil wipers made of cotton lamp wicking arranged so 
as to dip into oil reservoirs at each end of guides if they are 
horizontal, and at the lower end if they are vertical. These 
wipers will spread a film of oil over the guides at every stroke 
of the crosshead that will keep them well lubricated. 

79. Springing: of Bedplate. —If the bedplate of an 
engine is not rigid enough to resist the vibration of the moving 
parts, or if it is sprung from being set unevenly or by the 
unstable condition of the foundation, the engine will be thrown 
out of line either intermittently or permanently, and the bear¬ 
ings will heat; but it will do no good to refit the brasses unless 
the engine bed is stiffened in some way and leveled up if 
necessary. The form of the bedplate and foundation must 
generally suggest the best way to meet this difficulty. 

80. Bearing Spring or Shift. —The effect of the 
springing or shifting of the outboard bearing—that is, an outer 
bearing supported on the foundation away from the engine 


50 


GAS-ENGINE LUBRICATION 


frame—is similar to the springing of the engine bed; namely, 
the bearing will be thrown out of line, with the consequent 
danger of heating. As the pedestal forming the foot of the 
bearing is usually adjustable, it is an easy matter to readjust it, 
after which the holding-down bolts should be screwed down 
tight. This is one of the few instances where it is permissible 
for the engineer to use his strength on the wrench. As a rule, 
a nut or bolt should just be set up solid; with very rare excep¬ 
tions, a sledge hammer should not be used in driving a wrench, 
as 3-inch steel bolts have been broken in this way. It is also 
very bad practice to drive up a nut with a cold chisel and 
hammer, unless the nut is in a position where it is impossible to 
turn it with a wrench. 

If a pedestal is not stiff enough to resist the forces acting on 
it and it springs, measures should be taken to stiffen it. The 
method to be used can only be determined from the conditions, 
and calls for the exercise of judgment on the part of the 
engineer. 

81. Brasses Too Long-.— If the brasses are too long and 
bear against the collars of the journal when cold, they will 
surely heat after the engine has been running a short time; it 
is hardly possible to run bearings entirely cold, they will warm 
up a little and the brasses will be expanded thereby, which will 
cause them to bear still harder against the collars. This, in 
turn, will induce greater friction and more expansion of the 
brasses. 

This trouble may be overcome by filing a little off each end 
of the brasses until they cease to bear against the collars while 
running. A little side play is a good thing, since it promotes a 
better distribution of the oil and prevents the journal and 
brasses from wearing into grooves. 

82. Brasses Pinching the Journal at Their Edges. 

When first heated by abnormal friction, brasses tend to expand 
along the surface in contact with the journal; this will tend 
to open the brass and make the bore of larger diameter if it is 
not prevented by the cooler part near the outside and by the 
bedplate itself. 


GAS-ENGINE LUBRICATION 


51 


If the brass becomes hot very quickly, the resistance to 
expansion produces a permanent set of the metal near the 
journal, so that, on cooling, the brass closes and grips the 
journal; it will then set up sufficient friction to heat again and 
expand sufficiently to ease itself from the journal, and so long 
as that temperature is maintained the journal runs easily in 
the bearing. This is why some bearings always run somewhat 
warm and will not work cool. A continuance of heating and 
cooling will set up a mechanical action at the middle of the 
brass, which must eventually end in cracking it, just as a piece 
of sheet metal is broken by continually bending it backwards 
and forwards about a certain line. 

The heating by the brasses pinching the journal may be pre¬ 
vented by chipping off the brasses at their edges parallel to the 
journal, as shown at a and b, Fig. 28, 
in which c is a sectional view of the 
journal and d and e represent the 
top and bottom brasses. 

83. Brasses Set Up Too 
Tightly. —When the brasses of an 
engine bearing are set up too tightly, 
heating is inevitable, and probably 
more hot bearings result from this 
cause than from any other, and with 
less excuse. It is often the case that an attempt is made to stop 
a knocking or pounding in an engine by setting up the brasses 
when the pounding could and should be stopped in some other 
way. 

The direct cause of heating of bearings when the brasses are 
set up too tightly is the abnormal friction that is produced by 
the pressure of the brasses on the journal. The prevention and 
cure are obvious. The brasses should not be set up too tightly, 
and if they are, they should be slacked off as soon as possible. 
Hot bearings should never occur from this cause. Only a 
competent person should have charge of the bearings, and no 
one else should be permitted to adjust them. The bearings 
should be examined at the first signs of undue heating. 




52 


GAS-ENGINE LUBRICATION 


84. Brasses Too Loose. —Bearings may heat on account 
of the brasses being too loose. The heating is caused by the 
hammering of the journal against the brasses when the crank- 
pin is passing the dead centers. This fault is easily remedied, 
however, by setting up the cap nuts or key. Here the experi¬ 
ence and judgment of the engineer are called into play to 
decide just how much to set up, as it is very easy to overdo 
the matter and set up too far, with a hot bearing as the result. 

Most engineers have their own particular views regarding 
the setting up of bearings. One method is to set up the cap 
nuts tight and then slack them back a half turn; if the brasses 
are still too loose, they are set up again and slacked back less 
than before, repeating the operation until the ideal position is 
reached—that is, when there is neither pounding nor heating. 
It is important that this desired point be approached very 
gradually and carefully, else the chances are that it will be 
overreached and the operation will have to be repeated. 

85. Another method of setting up journal brasses is as 
follows: Fill up the spaces between the brasses with thin 
metal liners, say from 18 to 22 Birmingham wire gauge in 
thickness, and a few paper liners for fine adjustment; put in 
enough of them to cause the brasses to set rather loosely on 
the journal when the cap nuts or keys are set up solid. Run 
the engine for a while in that condition and note the effect; 
then take out a pair of the liners and set up solid again. 
Repeat this operation until there is neither thumping nor heat¬ 
ing. If this system of treating bearings is carefully carried 
out, there will be very little danger of their heating. When the 
proper adjustment is reached, the engine should run a long 
time without requiring any further adjustment of the bearings. 
In removing the liners, great care should be exercised not to 
disturb the brasses any more than is absolutely necessary, and 
to remove liners of equal thickness from each side. A pair 
of thin, flat-nosed pliers will be found useful in slipping out 
the liners. This method is preferable to the first one men¬ 
tioned, because there is not so much danger of setting the 
brasses up too far. 


GAS-ENGINE LUBRICATION 


53 


86. Brasses Warped and Cracked.— Warped and 
cracked brasses will cause heating, because they do not bear 
evenly on the journal, and hence the pressure is not distributed 
over the entire surface, as it should be. The remedy will 
depend on the extent of the distortion of the brasses. If the 
distortion is not too great, the brasses may be refitted to the 
journal by filing and scraping; but if they are twisted so much 
that they cannot be refitted, new brasses must be put in. 

87. Cut Brasses and Journals. —Brasses and journals 
that have been hot enough to be cut and grooved are liable 
to heat again at any time, on account of the undue friction pro¬ 
duced by the roughness of the wearing surfaces. As long as 
the grooves in the journal match the grooves in the brasses, the 
friction is not greatly increased; but if a smooth journal is 
placed between a set of brasses that are cut and pressure is 
applied, the journal crushes the ridges on the brasses, the 
friction becomes very great, and heating results. 

The way to prevent heating from this cause is to work the 
grooves out of the journal and brasses by filing and scraping as 
soon as possible after they occur. 

88. Oil Feed Stopped. —It does not take long for a 
bearing to get very hot if it is deprived of oil. The two prin¬ 
cipal causes of a bearing becoming dry are an oil cup that has 
stopped feeding, either because it is empty or because it is 
clogged by dirt in the oil, and oil holes and oil grooves closed 
by dirt or by the gumming of the oil. Both of these conditions 
are the direct result of negligence, and their existence can 
always be prevented by the exercise of reasonable care. 

In circulating constant-level splash oiling systems, as used in 
many automobile engines, the oil pump may have broken down, 
although with gear-pumps this defect is rather uncommon. 
More frequently the trouble is due to a broken oil-delivery 
pipe or a clogged oil inlet. When plunger pumps are used for 
circulating the oil, the pumps being submerged in oil all the 
time, the pumps may partly or entirely stop working, on account 
of dirt or a thread or two of waste finding its way to the 
suction-valve seats. If an oil pump of a circulating oiling 


54 


GAS-ENGINE LUBRICATION 


system is located above the oil reservoir, it may refuse to pump 
when the engine is started because it is air-bound, in which 
case it requires priming with oil in order to start it working. 

89. Oil Feed Insufficient.—The effect produced on a 
bearing by an insufficient oil supply is similar to that of no oil, 
only in a lesser degree. Of course it will take longer for a 
bearing to heat with insufficient oil than with none at all, and 
the engineer has more time in which to discover and remedy 
the difficulty. As a rule, however, more oil is used on bearings 
than is actually necessary, and a waste of oil is the result. A 
steady feed, a drop at a time, gives the best results. 

In automobile pressure-feed oiling systems of the high- 
pressure type, too low an oil pressure, due to wrong adjustment 
of the relief valve or a broken relief-valve spring, may be the 
cause of insufficient cylinder lubrication. In pressure-feed oil¬ 
ing systems not having an oil pump, insufficient lubrication is 
usually due to failure to keep sufficient oil in the reservoir; but 
it may be due to clogged oil screens, provided these are used. 
In the constant-level splash system the parts may get insuffi¬ 
cient lubrication because the oil in the splash troughs is not 
kept at the proper level due to lack of oil in the crank-case, or 
partial clogging of the feedpipes. 

90. Oil Unsuitable.—When a properly designed bear¬ 
ing is supplied with oil that is not suitable, that is, an oil that 
is too heavy or too light, a sufficient quantity cannot be retained 
in the bearing to lubricate it properly. Large quantities of thin 
oil may be fed to the bearing, but it will be squeezed and leav¬ 
ing only a thin film, and thus not properly lubricate the bearing. 
On the other hand, too-heavy oil will not enter the bearing in 
sufficient quantity to lubricate it properly. The effect of 
unsuitable oil is more pronounced in engines of the high-speed 
type, as used in automobiles, aeroplanes, etc., than in the slower 
running stationary type, although it is vitally important that oil 
of the proper quality be used in all cases. 

If gas-engine cylinder oil of the kind recommended by the 
maker of the car, such as is sold at retail in sealed cans and by 
reliable dealers, is used at all times for the engine, no trouble 


GAS-ENGINE LUBRICATION 


55 


on account of the oil itself will ever be experienced. If, how¬ 
ever, use is made of ordinary machine oil, lard oil, or steam- 
engine cylinder oil, which is usually bought because it is cheaper 
than gas-engine cylinder oils, trouble will be experienced almost 
immediately, and if this trouble is not attended to at once, the 
cylinders, pistons, and bearings may be ruined in a short time. 
Machine oil, lard oil, and steam-engine cylinder oil are excel¬ 
lent lubricants for the purpose for which they are intended, 
but they are utterly unsuitable for the lubrication of the high¬ 
speed gasoline engines used in automobiles. 

The trouble symptoms produced by the use of oil unsuited 
for lubricating the piston are white or yellow smoke in the 
exhaust, rapid fouling of spark plugs, partial clogging of inlet 
and exhaust valves, and rapid accumulation of carbon on the 
valves in the combustion chamber and about the piston rings. 

To remedy the trouble, inject kerosene freely through the 
priming cocks or spark-plug holes to loosen the carbon deposit 
on the piston rings, and use kerosene to free the valves if they 
stick. Drain the oil reservoir, and also the splash troughs in 
case of non-circulating constant-level splash system, and the 
crank-case if this does not form the oil reservoir; in short, 
drain all oil from the whole lubrication system and wash it 
out twice with kerosene. Drain off all kerosene and refill the 
oiling system with good gas-engine cylinder oil, not forgetting 
the splash troughs if they have to be filled separately. In case 
excessive carbonization has taken place in the cylinders, remove 
the carbon deposit. Then clean the spark plugs, and the engine 
will be ready again. 

91. Dirty and Gritty Oils, and Oils of Poor 
Quality. —Oils containing dirt and grit or that are deficient in 
lubricating quality causes hot bearings; but it is within the 
power of the engineer to guard against such causes. There is a 
great deal of dirt in lubricating oils of the average quality; 
therefore, all oil should be strained through a cloth or filtered, 
no matter how clear it looks. All oil cups, oil cans, and oil 
tubes and channels should frequently be thoroughly cleaned. 
Oil may be removed from the cups by means of an oil syringe. 


56 


GAS-ENGINE LUBRICATION 


All oil removed from the cups and cans should be strained or 
filtered before it is used. If these instructions are strictly 
followed, most of the danger of bearings heating from the 
use of dirty or gritty oils will be avoided. 

There is such a great variety of lubricating oils on the mar¬ 
ket whose quality cannot be definitely decided on without an 
actual trial that it is a difficult matter to avoid getting poor oil 
sometimes. About the only way to meet this trouble is to pay 
a fair price to a reliable dealer for oil that is known to be of 
good quality. Cheap oils are generally very deficient , in lubri¬ 
cating qualities, and hence should be avoided, as should also 
gummy oils, which choke the oil channels and cause the brasses 
and journals to stick together when the engine is stopped over 
night. 

92. Grit in Bearings. —Grit is an ever-present cause of 
heating of bearings; it is only by persistent effort on the part 
of the engineer that he can keep his machinery running cool in 
a dusty atmosphere. The causes of this condition are innumer¬ 
able; it is, therefore, only possible to mention a few of them 
here. Work done on a floor over an engine shakes dirt down 
upon it at some time or other; all floors over engines should 
therefore be made absolutely dust-proof by laying paper 
between the flooring. A prolific cause of hot bearings from 
grit in producer-gas engines, especially when the engine and 
producer rooms communicate, is carelessness in handling the 
ashes and clinkers. If piles of red-hot clinkers and ashes are 
deluged with buckets of water, the water is instantly con¬ 
verted into a large volume of steam that rises suddenly, carry¬ 
ing with it large quantities of small particles of ashes and grit 
that penetrate wherever it has access, and will find its way into 
the engine bearings. Throwing large quantities of water on 
hot clinkers and ashes should be avoided; sprinkle them instead, 
and close the producer-room door while the ashes and clinkers 
are being hauled or wet down or while the fire is being cleaned 
or hauled. 

93. If emery, emery cloth, Bath brick, or other gritty 
cleaning material is used about a bearing, it is sure to get 


GAS-ENGINE LUBRICATION 


57 


inside and cause trouble; it is, therefore, better not to use 
them close to a bearing. 

As a precaution against grit getting into a bearing, all open 
oil holes should be closed with wooden plugs or clean cotton 
waste as soon as possible after the engine is stopped, and 
should be kept closed until ready to oil the engine again pre¬ 
paratory to starting up. Plaited hemp or other suitable cover¬ 
ing should also be laid over the spaces between the ends of the 
brasses and the collars of the journals of every bearing on the 
engine and kept there while the engine is standing still. 

Bearings are now in use that, it is claimed by their makers, 
are dust-proof, but their use does not relieve the engineer from 
the responsibility of taking every precaution possible to keep 
grit and dirt out of the bearings of his engine. 

94. Premature Ignition.— Bearings designed to stand 
a given amount of pressure will begin to heat if this pressure is 
greatly and constantly exceeded. Premature ignition of the 
incoming charge caused by various conditions will result in 
abnormally high initial pressure and severe shocks upon the 
bearings. Experience shows that the crankpin especially will 
heat under such conditions. The remedy consists in finding 
the actual cause of the premature firing and using the proper 
means to stop it. 

95. Journals Too Small. —Journals that have insuffi¬ 
cient area of wearing surface will heat. In practice, only a 
certain amount of pressure per square inch of area can be sus¬ 
tained by a bearing before the friction reaches the point that 
will cause heating. 

The pressure that a bearing will sustain per square inch of 
area of rubbing surface without heating depends on the mate¬ 
rials of which the journal and brasses are composed, the fine¬ 
ness of their finish, the accuracy of their fit, the adjustment of 
the brasses, and the lubricant used. 

Pressure and friction have a direct relation to each other. 
The total amount of friction of two bodies in contact depends 
on the pressure of the one on the other and is nearly indepen¬ 
dent of the area of the surfaces in contact. The total pressure 


58 


GAS-ENGINE LUBRICATION 


on the bearing divided by the projected area, that is, the prod¬ 
uct of the length and the diameter of the bearing, in inches, 
gives the bearing pressure per square inch. If the allowable 
bearing pressure per square inch is exceeded, heating is liable 
to occur, for the heating is proportional to the friction pro¬ 
duced, and the friction per square inch depends on the bearing 
pressure per square inch. Hence, less friction is produced per 
square inch of surface by a long journal than by a short one of 
equal diameter with the same total pressure; therefore, a long 
journal is not nearly so liable to heat as a short one of the 
same diameter, and a journal of large diameter is not so liable 
to heat as one of small diameter of equal length. It is the aim 
of the designer so to proportion the journal that the pressure 
per square inch of bearing surface shall not exceed the safe 
limit for the given conditions. 

There is only one cure for a bearing that heats constantly 
because it is too small, and that is to make it larger if circum¬ 
stances permit this to be done. If this is impossible the best 
of lubrication must be used, and, if necessary, water must be 
run constantly on the bearing. 

96. Overloaded Engines. —The effect produced by 
overloading an engine is similar to that when the journal is 
too small. The pressure on the brasses being increased to a 
point beyond that for which they were designed, the friction 
exceeds the practical limit and the bearing heats. The only 
thing to do to remedy this difficulty is to reduce the load on the 
engine. 

When an engine is being run under a load that is near or 
equal to the maximum for which it is designed, it is wise to 
keep a set of new brasses on hand, to be put in place when 
required. This .precaution is especially important in a plant 
where the shutting down of the engine for any great length of 
time will incur a large loss, and it should be observed espe¬ 
cially if it is known that the journals are too small, or the 
engine is somewhat overloaded. 

97. External Heat. —Bearings may get hot from exter¬ 
nal heat. This may be the case if the engine is placed too near 


GAS-ENGINE LUBRICATION 


59 


furnaces or in an atmosphere heated by uncovered steam pipes 
or other means. The excessive heat of the atmosphere will 
then expand the brasses until they bind on the journals, which 
will generate additional heat and cause further expansion of 
the brasses, resulting in a hot bearing. 

If the engine is placed close enough to a furnace to cause 
heating from that source, a tight partition should be put up 
between them, if possible; this will also prevent dirt and grit 
from the furnace from getting into the bearings. If steam 
pipes in the room are bare, they should be covered with some 
good non-conducting material; and in some cases ventilating 
fans may be used to advantage. Other remedies depend on 
the conditions and require the judgment of the engineer. 


7 













Serial 1861 


CARBURETERS 


Edition 1 


FORMATION OF EXPLOSIVE MIXTURES 


EFFECTS OF CHANGES IN PROPORTIONS 

1. An explosion is an extremely rapid burning of a sub¬ 
stance, and is accompanied by the formation of gases and a 
considerable increase of pressure. Any mixture of two or 
more substances that will burn in this way is called an explo¬ 
sive mixture, or simply an explosive. The mixture of 
gasoline vapor and air in the cylinder of a gasoline engine is a 
familiar example of an explosive mixture. The burning is 
started by means of an electric spark, and the explosion that 
results raises the pressure of the gases in the cylinder. The 
pressure of these gases pushes the piston forwards in the 
cylinder and so enables the engine to do work. 

2. The operation of setting fire to the gaseous mixture in 
the engine cylinder by means of a device called an igniter or a 
spark plug is known as ignition. The moment that ignition 
begins is called the time of ignition. The quantity of the mix¬ 
ture of gas and air taken into the cylinder at one time is called 
the charge, and when all of it is ignited, it is said to be 
wholly inflamed. The time elapsing betwen the time of igni¬ 
tion and the moment when the gas is wholly inflamed is known 
as the duration of inflammation , or duration of the explosion. 
The velocity with which the flame is generated in the charge is 
called the rate of flame propagation. 

3. When the burning mixture has reached its greatest 
pressure, a short time may elapse before the pressure begins to 


COPYRIGHTED BY INTERNATIONA!. TEXTBOOK COMPANY. ALL RIGHTS RESERVED 




2 


CARBURETERS 


fall to that of the atmosphere. This time is called the duration 
of maximum pressure. The time from the moment when the 
pressure commences its fall from the maximum pressure to 
the moment when the pressure reaches that of the atmosphere 
is known as the duration of fall of pressure. The velocity with 
which this fall of pressure takes place is the rate of fall of 
pressure. 

4. Gases available for engine purposes vary so much in 
their behavior when ignited in the gas-engine cylinder that a 
knowledge of their performance is of great value to the opera¬ 
tor. Certain effects are produced when an explosive mixture 
is confined in a closed vessel without the opportunity of expan¬ 
sion such as it has in the gas engine. These effects relate to 
inflammation of the gas, duration of maximum pressure, and 
rate of fall of pressure. The relation of these to the propor¬ 
tions of gas and air in the cylinder of a gas engine is very 
important. 

5. The relative proportions of gas and air in the charge 
affect the duration of inflammation, the rate of flame propaga¬ 
tion, the duration of maximum pressure, and the rate of fall 
of pressure. To learn something of the effects produced by 
changes in the quality of the mixture, a number of experi¬ 
ments were made, using a cast-iron explosion chamber 7 inches 
in diameter and inches long. Explosive mixtures of differ¬ 
ent qualities were introduced into the chamber and ignited, and 
a recording instrument similar to an indicator was used to 
show the change of pressure that resulted. There was no 
piston in the cylindrical explosion chamber and consequently no 
expansion of the gases could occur. Instead, the pressure 
decreased as the heat of explosion was conducted away by 
the metal walls. The mixtures used varied from 14 parts of 
air and 1 part of gas to 4 parts of air and 1 part of gas, by 
volume. The mixture containing a large volume of air to a 
small volume of gas is a lean mixture and that containing more 
nearly equal volumes of air and gas is a rich mixture. The 
pressures obtained from these various mixtures are given in 
Table I. 


CARBURETERS 


3 


6 . The rate of flame propagation is measured approxi¬ 
mately by the time from the moment of ignition to the moment 
at which the maximum pressure is reached. In the experiments 
referred to, the rate of flame propagation was greatest in the 
mixture containing 6 volumes of air to 1 volume of gas. As 
the mixture was made leaner by increasing the proportion of 
air, the rate of flame propagation became lower; that is, the 
mixture burned more slowly as the proportion of air was 
increased, and the maximum pressure was not reached so 


TABLE I 

PROPORTIONS OF MIXTURES AND RESULTING PRESSURES 


Volumes of Air to 
i Volume of Gas 

Proportion of Gas in 
Mixture 

Maximum Pressure 
per Square Inch 

Area of Piston to 
Each Cubic Inch of 
Gas 

Total Maximum Pres¬ 
sure per Cubic Inch 
of Gas 

Pressure per Square 
Inch .2 Second After 
Maximum 

Pressure Total to 
Each Cubic Inch of 
Gas, .2 Second After 
Maximum 

Mean Pressure on 

Piston During the 

First .2 Second 

14 

T5 

40 

15 

6oo 

31 

465 

532 

13 

Ti 

5 i -5 

14 

/2I 

40 

560 

640 

12 

T3 

6o 

13 

780 

42 

546 

663 

II 

T2- 

6i 

12 

732 

44 

528 

630 

9 

Tfr 

78 

10 

780 

44 

44O 

6lO 

7 

£ 

87 

8 

696 

47 

376 

536 

6 

T 

90 

7 

630 

52 

364 

497 

5 

l 

6 

9 i 

6 

546 

50 

300 

423 

4 

1 

5 

8o 

5 

400 

46 

230 

315 


soon. On the other hand, the rate of fall of pressure was less 
rapid, and the gases had a higher pressure at the end of 
1 second than was the case with gases resulting from the burn¬ 
ing of richer mixtures. Mixtures richer than the one con¬ 
taining 6 volumes of air to 1 of gas had slower rates of flame 
propagation than the 6-to-l mixture, indicating that the burn¬ 
ing was most rapid with proportions of about 6 of air to 1 of 
gas. 

7. The best proportions of gas and air to use for any gas, 
in an engine having no compression, is not usually that which 



















4 


CARBURETERS 


has the greatest explosive power. The best proportion is that 
which gives the highest pressure for the quantity of gas used. 
For the purpose of illustration, suppose that the distance 
between the end of the cylinder and the end of the piston is 
exactly 1 inch; then, for each cubic inch contained in this 
space, there will be 1 square inch on the surface of the piston. 
The mixture that will give the highest pressure for the same 
quantity of gas can be calculated as follows: For instance, 
take the mixture containing one volume of gas to five volumes 
of air. In Table I, in which the results of the before-described 
experiments are tabulated, the maximum pressure for this 
mixture is given as 91 pounds per square inch. Since there 
are five volumes of air and one volume of gas, for each cubic 
inch of gas there will be six volumes of the mixture; and to 
each cubic inch of gas, in a layer 1 inch deep, there will be 
6 square inches of the mixture. Hence, the pressure of 
91 pounds per square inch is exerted on 6 square inches, and 
the total pressure exerted by each cubic inch of gas is 91X6 
= 546 pounds. 

The mixtures giving the highest pressure for 1 cubic inch 
of gas are seen to be those having one volume of gas to twelve 
of air, and one volume of gas to nine of air. 

8. The mixture giving the best average pressure for the 
first .2 second is that giving 663 pounds to each cubic inch of 
gas, or the mixture containing one volume of gas to twelve 
volumes of air. If the power stroke could be considered as 
taking place without increasing the volume of the space 
occupied by the gaseous mixture, the pressure remaining at 
the end of .2 second after the maximum pressure has been 
reached would be that given in the seventh column, and the 
mean, or average, pressure at the end of .2 second after explo¬ 
sion would be that given in the last column. The last column 
gives a means of comparison of the power to be obtained in 
using the mixtures indicated in the first column. Thus, the 
mixture having one volume of gas to thirteen of air is more 
than twice as powerful as that having one volume of gas to 
four volumes of air, or in the ratio of 640 to 315, considering 


CARBURETERS 


5 


the power available during the first .2 second after explosion. 
Of course, there is no such thing as an engine running without 
increasing the volume of the gases, but this assumption is 
made in order to give a method of comparing the various 
mixtures. 

9. The conditions under which these experiments were 
carried out are not those under which combustion takes place 
in an engine cylinder; but the results given will serve to 
indicate, to some extent, the effect of changing the quality of 
the charge in an internal-combustion engine. In an actual 
engine the charge is compressed before ignition takes place, 
and the result is that the rate of flame propagation is very 
greatly increased. Moreover, ignition is so timed that the 
point of maximum pressure occurs at the end of the stroke. 
The rate of fall of pressure is more rapid, because the gases 
expand as the piston moves forwards; therefore, there is loss 
of heat from the gases, not only by the cooling effect of the 
walls, but also by the conversion of heat into work during 
expansion. 


DEVICES FOR MAKING EXPLOSIVE MIXTURES 


CARBURETERS FOR STATIONARY ENGINES 

10. The explosive mixture in the cylinder of an internal- 
combustion engine must be composed of gas and air or of 
vapor and air in such proportions that it will burn when once 
ignited. If the fuel used is a gas, such as producer gas or 
blast-furnace gas, the explosive mixture is made by admitting 
the correct proportions of gas and air to the cylinder through 
a mixing valve. The object of the mixing valve is to cause 
the gas and the air to mix thoroughly, so that combustion will 
be rapid and complete. If the fuel used is a liquid, such as 
gasoline or kerosene, there is greater difficulty in forming the 
explosive mixture. Liquid fuels will not burn while they 
remain liquid. Befofe liquid fuel can be burned, it must be 
changed to a vapor or a gas, and then the vapor or the gas 




6 


CARBURETERS 


must be mixed with air in the proper proportions to form a 
combustible mixture. The device that is used to change the 
liquid to a gas or to a vapor is called a carbureter or a 
vaporizer. 

11. Heat must always be added to a liquid in order to 
change it to a gaseous form. If the quantity of heat necessary 
to vaporize a given quantity of liquid is comparatively small, 
the liquid is said to be volatile. Gasoline is a familiar form of 
volatile liquid, and of all the liquid fuels used in internal- 
combustion engines, it is the most easily vaporized. The pas¬ 
sage of a current of air at ordinary temperatures over the 

surface of gasoline is 
sufficient to cause va¬ 
porization of a part of 
the liquid and to pro¬ 
duce an explosive mix¬ 
ture with the air. The 
heat required to cause 
the vaporization in such 
a case is contained in 
the air that passes over 
the gasoline. With less 
volatile oils, such as 
kerosene, distillate, and 
crude oil, greater difficulty is experienced in obtaining satisfac¬ 
tory vaporization and mixing with air; therefore, carbureters 
used for vaporizing gasoline will be described first. 

12. The most widely used form of carbureter for gasoline 
is the spray carbureter, so called because it injects a jet or 
spray of gasoline into the air-current that passes through the 
carbureter on its way to the cylinder of the engine. The prin¬ 
ciple on which the jet carbureter acts may readily be under¬ 
stood by reference to Fig. 1. This illustration does not show 
an actual form of carbureter, but simply represents the essential 
parts. The gasoline is contained in a tank a, from which it 
flows through a suitable passage to a nozzle b, the tip of which 











































CARBURETERS 


7 


is at the level of the surface of the gasoline in the tank. The 
nozzle b is in the center of a pipe c that leads to a cylinder d in 
which is fitted a piston e. If the piston is drawn upwards 
suddenly, a partial vacuum will be formed in the cylinder d 
and air will rush up the tube c past the nozzle b. The suction 
thus produced around the nozzle will cause some of the gasoline 
to be drawn out in the form of a spray, as shown, and the spray 
will be taken up by the air-current and carried on into the 
cylinder d. 

13. In actual service, the suction that causes the flow of air 
through the carbureter is due to the outward, or downward, 
movement of the piston in the engine cylinder, a partial vacuum 
thus being produced in the cylinder. The spray of gasoline 
thrown into the air-current in the carbureter is carried along by 
the air into the cylinder through a suitable pipe connecting the 
carbureter with the cylinder, and during this travel the finely 
divided spray evaporates into gasoline vapor. The result is 
that the air and the vapor enter the cylinder thoroughly mixed, 
and form an explosive mixture. If the carbureter were 
actually made like that shown in Fig. 1, the suction of gasoline 
from the nozzle b would eventually lower the level in the tank 
until no more fuel could be drawn out of the nozzle. In the 
forms of carbureters in use on engines, therefore, some means 
is provided whereby the level of the gasoline in the reservoir 
and the nozzle is maintained. 

14. One very common way of maintaining a constant level 
of gasoline in a carbureter is by the use of a float, such a 
device being known as a float-feed carbureter. The prin¬ 
ciple of construction of a float-feed carbureter is shown in 
Fig. 2. Fuel from the supply tank enters the bottom of the 
carbureter at a and flows up past the valve b into the float 
chamber c, which must not be perfectly air-tight above the 
float. Part of the fuel flows into the passage leading to the 
spray nozzle d. As the fuel rises in the float chamber it lifts 
the float e and also the valve b attached to the float. When the 
fuel reaches a level slightly below the top of the spray nozzle d. 


8 


CARBURETERS 


the valve b closes the inlet passage to the float chamber and thus 
stops the inflow of gasoline. The upper end of the chamber h 
is connected to the engine intake. The suction of the engine 
draws in air at the opening / of the air passage g, past the 
nozzle d, with considerable velocity, into the mixing chamber h 
and out at the top, as indicated by the arrows. On account of 
the velocity of the air passing the nozzle d, and the suction at d, 
which is lower than that upon the surface of the fuel in the 
float chamber c, fuel is drawn out from the spray nozzle; the 
float e therefore descends slightly by the lowering of the fuel 
in the float chamber, and the float valve b is slightly opened, so 
as to allow more fuel to enter and thus maintain a nearly 

constant level in the 
float chamber. Either 
a hollow metallic float 
or a cork float may be 
used. 

13. The vaporiza¬ 
tion of the fuel re¬ 
quires heat, part of 
which is drawn from 
the walls of the air 
passage or mixing 
chamber h, Fig. 2. 
This withdrawal of 
heat leaves the metal 
around the air pas¬ 
sage cold, even at 
times below the freezing point of water. The coldness retards 
the rapidity of vaporization, and in some cases interferes with 
the satisfactory operation of the carbureter. In order to 
prevent this, a jacket space i may be provided around the mix¬ 
ing chamber, and exhaust gas from the engine or water from 
the cylinder water-jackets may be circulated through this 
jacket space to keep the carbureter warm. 

16. A very simple form of mixer, used on engines of 
small power, is that shown ir> section in Fig. 3. The casting a 


























































CARBURETERS 


9 


forming the body of the mixer is attached to the top of the 
gasoline tank b. A pipe c leads from the opening d to a point 
beneath the level of the gaso¬ 
line and carries at its lower 
end a cage e containing the 
ball check-valve /. A needle 
valve g having a knurled 
head h is used to regulate the 
amount of opening at d. Air 
is drawn in at i on the suction 
stroke of the engine and passes 
the needle valve g on its way 
to the cylinder, which is con¬ 
nected at j. The partial 
vacuum formed in the mixing 
chamber k causes gasoline to 
be drawn up in the pipe c and 
out through the opening d past 
the needle valve. As soon 
as the suction ceases, the gasoline tends to run down the pipe c 
and back into the tank; but the ball / drops to its seat and 
prevents any flow downwards. The pipe c is thus kept full of 





gasoline at all times, and the amount of gasoline fed is reg¬ 
ulated by adjusting the needle valve g. The needle valve 





















































10 


CARBURETERS 


should be set with the least opening that will suffice to keep the 
engine running smoothly under its normal load. 

17. Still another method of keeping the level of the 
gasoline in the carbureter fairly constant is to provide an over¬ 
flow, and to use a pump to force the gasoline into the car¬ 
bureter. A form of carbureter in which the level is maintained 
in this way is shown in section in Fig. 4 (a) and ( b ). The 

gasoline is pumped into 
the fuel reservoir a through 
the pipe b. As soon as the 
reservoir is filled to the 
level of the top of the par¬ 
tition c, any extra amount 
supplied by the pump runs 
over the partition into the 
chamber d and is drained 
back to the tank through 
the pipe e. A passage / 
leads from the reservoir a 
to the needle valve g by 
which the flow of gasoline 
is regulated. The air enters 
at h and is drawn past the 
nozzle i on its way to the 
cylinder. The suction thus 
produced draws the gaso¬ 
line out past the needle 
valve. The face j of the 
carbureter is bolted against the side of the engine cylinder by 
means of bolts k that pass through the carbureter casting, and 
the nozzle i projects into the passage leading to the inlet valve. 
The air chamber / above and around the nozzle also opens into 
this passage, and thus the air flowing past the nozzle i carries 
the fuel into the cylinder. 



Fig. 5 


18. A form of fuel pump is shown in section in Fig. 5. 
The body a is formed with two valve seats on which rest the 
ball valves b and c, and a passage d leads from one valve to 


















CARBURETERS 


11 


the other. At the middle of the pump is a plunger e that is 
given an up-and-down motion from some part of the engine. 
A suction pipe attached at f leads to the fuel tank, and a dis¬ 
charge pipe connected at g leads to the carbureter. When the 
plunger is moved upwards a partial vacuum is created in the 
passage d, and fuel is drawn up from the tank past the valve c 
into the passage. The valve b is held closed by the pressure that 
acts on top of it. As soon as the plunger starts to descend, the 
valve c drops to its seat, and the fuel cannot return to the tank. 
A pressure is thus produced in the passage d, causing the 
valve b to rise, and the fuel is forced out into the pipe at g and 
so to the carbureter. At the end of the downward stroke the 
valve b closes, and the fuel is prevented from running back 
into the pump from the carbureter. The plunger is surrounded 
by packing h that is compressed by a gland i held down by the 
nut j. A tight joint is thus made and leakage is prevented. 

19. The great trouble experienced with engines using 
kerosene as fuel is that kerosene is less volatile than gasoline 
and is therefore much more difficult to vaporize. It is possible 
to spray kerosene into the air-current with an ordinary car¬ 
bureter such as is used for gasoline; but the finely divided 
particles of kerosene will not change to vapor readily and are 
apt to be carried into the engine cylinder as spray. Once they 
have entered the cylinder, the heat of the metal walls and the 
heat developed during compression may be sufficient to change 
all of the spray to vapor, in which case the engine will work 
satisfactorily; but if the heat is not great enough to vaporize 
the kerosene completely, and the charge is fired while some of 
the fuel is still in the liquid form, the burning will not be per¬ 
fect and trouble will result.. The outer layers of the drops of 
kerosene spray will be vaporized by the heat of the explosion 
and will burn, but the centers will not, because they remain 
liquid, and the liquid will be changed by the heat to carbon 
and a sort of tar, both of which will be deposited on the cylin¬ 
der, the piston, the spark plugs, and the exhaust passages, 
fouling them and necessitating frequent cleaning. The exhaust 
gases will be smoky and will have a very offensive smell. 


12 


CARBURETERS 


20. To overcome the difficulties met with in the vaporiza¬ 
tion of kerosene, the plan of heating the air supply has been 
adopted. The heated air, on meeting the spray of kerosene, 
gives up its heat and thus causes the spray to vaporize much 
more rapidly than would be the case if the air were at an ordi¬ 
nary temperature. Another method is to heat the kerosene 
before it leaves the spray nozzle. This may be done by sur¬ 
rounding the fuel reservoir with a jacket through which hot 
water from the water-jacket is circulated. A third way of 
improving the vaporization of kerosene is to spray it in a finer 
form, so that the liquid particles will be much smaller and thus 
more readily converted into vapor. The injection of water 
vapor into the cylinder along with the charge of air and vapor 
has been found to improve the action of the kerosene engine. 
The water vapor is changed to steam by the heat of the burning 
charge, and thus lowers the temperature in the cylinder some¬ 
what, and prevents pounding. It also prevents the deposit of 
carbon and tar, and the inside of the cylinder stays clean. 
Many engines that use kerosene as fuel are so arranged that 
they can be started on gasoline, which is used until the engine 
is warm enough to run on kerosene. 

21 , A form of vaporizer for an engine using kerosene is 
shown partly in section in Fig. 6, in which (a) is the arrange¬ 
ment for running the engine on gasoline and (b) is the arrange¬ 
ment for regular running on kerosene. The gasoline is stored 
in a small tank a on top of the kerosene tank b, and each tank 
is connected to the supply pipe c that leads to the spray nozzle d. 
The amount of opening of the nozzle is regulated by the needle 
valve e . When the engine is to be started on gasoline, the 
cylindrical shutter / is turned so that the web on its outer end 
is horizontal, with the word GASOLINE at the top, as shown 
in (a). The air supply is then drawn in at g, through the 
opening h in the side of the shutter, and so out past the spray 
nozzle. The kerosene valve i is closed and the gasoline valve j 
is open, and so the suction draws gasoline from the spray 
nozzle and carries it along with the air into the mixing cham¬ 
ber k and thence through the inlet valve l into the cylinder. 


CARBURETERS 


13 


22. After the engine has been running on gasoline until it 
is thoroughly warmed up, the shutter /, Fig. 6, is given a quick 
turn half-way around, bringing the word KEROSENE on top 




Fig. 6 

as shown in (6). The air opening g is thus closed and the 
opening h is brought over the top of the passage m, which 
leads from the chamber n formed inside the sleeve o and 
around the exhaust pipe b. The exhaust gases are discharged 






































14 


CARBURETERS 


from the cylinder through the inner pipe p into the muffler q. 
The air supply is drawn in at the opening r between the sleeve o 
and the pipe p and passes along the chamber n into the pas¬ 
sage m and thence past the spray nozzle to the mixing chamber. 
In passing over the hot exhaust pipe p the air is heated and the 
fuel is thus vaporized far more easily and rapidly. If the 
engine begins to pound when the change to hot air is made, 
the valve s should be opened slowly. Hot water will then flow 
from the tank t through the pipe u and into the passage m 
through the nozzle v. This water will be sprayed by the cur¬ 
rent of air and will be carried into the cylinder. As soon as 
the valve ^ is opened so as to admit the proper quantity of 
water, the pounding will cease. 

23. The engine should be allowed to run for several 
minutes on gasoline and hot air, with the water-injection valve 
open. Then the gasoline valve j, Fig. 6, should be closed about 
half way and the kerosene valve i should be opened. As both 
fuel tanks are then in communication with the supply pipe c, 
the fuel drawn past the spray nozzle will be a mixture of 
gasoline and kerosene. After the engine has been running for 
a few minutes on the mixture of both fuels, the valve j may be 
closed completely and the operation will continue on kerosene 
alone. The needle valve e should be adjusted until the explo¬ 
sions are regular. It is probable that a somewhat greater open¬ 
ing of the valve will be required when using kerosene than 
when using gasoline. The water valve s must be handled 
carefully and only enough water should be admitted to stop 
the pounding. If too much water is admitted, the engine will 
stop. 

The foregoing explanation applies particularly to the type of 
combined gasoline and kerosene carbureter illustrated. There 
are other forms of combined carbureters that differ in details of 
construction and operation from that shown. In general, 
however, the principle of action is the same; that is, the engine 
is started on gasoline and warmed up, and then the change 
to kerosene is made by manipulating the valves in the fuel 
pipes. 


CARBURETERS 


15 



24. The vaporizer shown in Fig. 7 (a) and (b) is called a 
mixing: valve and is intended for use on stationary engines 
running on kerosene as fuel. There are two pipe connections, 
that at a for the kerosene 
pipe and that at b for the 
water pipe. From the con¬ 
nection a, a passage c leads 
to a spray opening d that is 
regulated by a needle valve 
c. A similar passage leads 
from the water connection 
to another spray opening 
controlled by the needle 
valve f. Both of the spray 
openings are in the beveled 
seat g of the valve h, so 
that, when the valve is 
closed, the spray openings 
are covered by the edge of 
the valve disk. A light 
spring i on the lower end of 
the valve stem holds the 
valve to its seat except on 
the suction stroke of the 
piston, when a vacuum is 
formed in the mixing cham¬ 
ber /. The pressure of the 
atmosphere on the under 
side of the valve h lifts the 
valve, and air is drawn 
through from the opening k 
past the spray nozzles into 
the mixing chamber and 
thence out to the cylinder 
by way of a pipe connected 
at /. As soon as the valve h is lifted, the vacuum causes 
kerosene and water to be sprayed from the spray openings, 
and the air-current picks up the spray and carries it into the 



356—8 

















1G 


CARBURETERS 



Fig. 8 


cylinder. The connections a and b are alike, and either can be 
used for fuel or water. If they are interchanged, the removable 

indicators m and n should 
be transposed. 

25. A mixing valve for 
use on small gasoline en¬ 
gines is shown partly in 
section in Fig. 8. The con¬ 
struction is very much like 
that of the kerosene mixing 
valve just described. There 
is but one fuel inlet a, from 
which the gasoline flows 
through a passage to the 
chamber b, and through 
the opening c controlled by 
the needle valve d. The valve opening c is in the seat of the 
valve e, and this valve lifts only during the suction stroke of 
the piston of the engine. The flow of gasoline is checked, 
therefore, whenever the valve e is seated. The gasoline may 
be fed from a constant-level chamber or it may be fed under 
slight pressure by having the reservoir slightly above the 
level of the spray opening. As a rule, a mixing valve does 
not give as perfect a mixture 
as does a carbureter with a 
nozzle; but if it is used on a 
two-cycle engine with crank¬ 
case compression a better 
mixture can be obtained, be- 
cause the gas and the air will 
be more thoroughly mixed 
while passing through the 
crank-case. 


26. A very simple form 
of gasoline mixing valve for Fig * 9 

use on engines of small power is shown in Fig. 9. The gasoline 
is maintained at a constant level in the reservoir cl bv means of 































CARBURETERS 


17 


a pump and an overflow pipe not shown, but similar to those 
already described. The gasoline enters the chamber a from the 
pipe i through an opening protected by fine wire gauze. The 
air is drawn in at b and passes the mouth of the spray opening c 
on its way to the cylinder. Gasoline is sucked up the passage d 
and is sprayed into the air-current past the needle valve e, the 
mixture leaving the mixing valve at /. The post, or pointer, g 
enables the needle valve to be set to certain known positions to 
correspond to different running conditions. A sliding damper h 
is placed at the air 
inlet to make starting 
easy. When the en¬ 
gine is to be started, 
the damper is placed 
so as to close the air 
inlet. The first suc¬ 
tion stroke of the pis¬ 
ton will then draw a 
rich charge into the 
cylinder. As soon as 
the engine has started, 
the damper is opened 
and the air permitted 
to enter the air inlet 
freely. 

27. The carbureter 
shown in Fig. 10 is 
built especially for 
use with a two-cycle engine. The fuel flows from the supply 
tank through the pipe a to the float chamber b, in which a con¬ 
stant level is maintained by a cork float attached to the stem of 
the valve c ; the float chamber is surrounded by glass, so that 
the gasoline level can be seen. From the top of the float 
chamber, a pipe d leads to the port e near the bottom of the 
engine cylinder, and from the bottom of the chamber a pipe f 
leads to the spray nozzle g governed by the needle valve h. A 
tube i leads from the spray nozzle to the inlet port j of the 



Fig. 10 



































18 


CARBURETERS 


cylinder. When the piston k moves upwards and uncovers the 
port e, the partial vacuum created in the crank-case is trans¬ 
mitted to the float chamber through the pipe d, and the suction 
draws fuel up from the supply tank. On the downward stroke 
of the piston a pressure is created in the crank-case, and con¬ 
sequently in the float chamber; but the fuel cannot flow back to 
the tank, because the ball check-valve l seats'itself under the 
pressure from above. The result is that, as soon as the port j 
is uncovered, the pressure on the fuel in the float chamber 
forces some of the fuel past the needle valve and through the 
tube i into the cylinder, where it strikes the hot deflector m on 
the top of the piston and is rapidly vaporized. At the same 
time, compressed air from the crank¬ 
case flows through the pipe n into the 
cylinder by way of the port j and 
mixes with the vaporized spray. A 
shutter that can be moved by the 
handle o is placed in the upper end of 
the air pipe n to regulate the amount 
of air admitted to the cylinder. 

28. Another very simple design 
of carbureter is shown in section in 
Fig. 11. The body a consists of a 
right-angled bend, on the back of 
which is cast the fuel reservoir b. The 
fuel is maintained at a constant level by means of a force pump 
and an overflow pipe, which are not shown but which are like 
those already described. The carbureter is bolted to the cylin¬ 
der at c and the air enters through the opening d. The spray 
nozzle is a bent tube e, the tip of which is central in the air pipe 
and the lower end of which communicates with the passage f 
leading to the fuel reservoir. A needle valve g controls the rate 
of flow of fuel to the spray nozzle. The plug h may be removed 
when it becomes necessary to clean the passage /. 

29. Inasmuch as the spray of fuel is drawn out of the 
nozzle by the suction caused by the rush of air past the nozzle, 



























CARBURETERS 


19 


a strong suction at the tip of the nozzle is desirable. To 
increase the suction, the tube in which the nozzle is located is 
often made of a special form, known as a Venturi tube. The 
Venturi tube, as shown diagrammatically in Fig. 12, consists 
of two tapering tubes joined at their small ends so as to form a 
continuous tube. A fluid entering at a. and flowing in the 
direction of the arrow, 
passes first through a 
rapidly narrowing part 
until it reaches the nar¬ 
rowest cross-section at b, 
known as the throat, and 
then passes through a gradually widening part to the discharge 
orifice at c. This form of tube derives its name from an Italian 
named Venturi, who experimented with various modifications 
of it and discovered certain peculiar facts with reference to its 
influence on the rate of flow and the quantity of discharge of 
fluids passing through it. 

30. When a fluid under constant pressure flows through a 
short tube of uniform diameter, the velocity of flow is prac¬ 
tically the same at all points; but when the flow occurs in a 
Venturi tube, the velocity varies, being least at the cross-section 
of greatest area and greatest at the cross-section of least area. 
In Fig. 12, the flow of fluid through the tube in the direction 
from a to c results in the formation of a slight vacuum just 
beyond the throat d, and if a small pipe e were attached at this 
point, as shown, air would be drawn in through it. In other 
words, the pressure at a point just beyond the throat is less 
than the pressure outside the Venturi tube. On account of this 
peculiar action, the velocity of flow through the throat of a 
Venturi tube is greater than that through a straight pipe of 
equal diameter, under the same conditions as to pressure, and 
so the discharge from the Venturi tube is also greater. 

31. The method of applying the principle of the Venturi 
tube to a carbureter may be illustrated by the diagram in 
Fig. 13. The main air supply to the carbureter enters at a, 
passes to the throat b of the Venturi tube and flows through 







Fig. 12 




20 


CARBURETERS 


the expanding passage c to the engine. The gasoline is sup¬ 
plied to the spray nozzle d, which is inserted into the lower end 
of the Venturi tube and is of such length that the opening e is 
central in the tube at a point just beyond the throat. In other 
words, the upper end of the nozzle d is located at the point 
where the pressure is least, so that, when the carbureter is 
working, the gasoline is discharged from the opening e into a 
partial vacuum, thus insuring a greater flow. 

32. The gasoline in the float chamber to which the nozzle d, 
Fig. 13, is connected is acted on by atmospheric pressure, or 
about 15 pounds per square inch at sea level; whereas, the 

gasoline issuing from the orifice e is subjected to 
a pressure that may be less by several pounds per 
square inch. As a result of these unbalanced 
pressures, the gasoline is forced rapidly through 
the nozzle d and is discharged from the orifice e 
in the form of spray, which is caught up by the 
air supply and carried on toward the mixing 
chamber. The reduction of pressure at the end 
of the nozzle d also insures a more rapid vaporiza¬ 
tion of the gasoline. It is a well-known fact that 
the temperature at which a liquid boils and 
changes into vapor is lowered by reducing the 
pressure on the liquid. Thus, water will boil at 
a temperature of 212° F. at sea level; but at the 
top of a mountain 1 mile above sea level, where 
the pressure is less because the air is rarer, water will boil at 
202° F. Similarly, when the gasoline is discharged into the 
throat b, where the pressure is reduced, its boiling point is 
lowered considerably and the result is that it flashes into vapor 
much more readily than when subjected to atmospheric 
pressure. 

33. The flow of gasoline from the spray nozzle does not 
increase or decrease in proportion to the increase or decrease of 
flow of air through the Venturi tube. As the suction increases, 
due to greater engine speed, the flow of gasoline increases more 
rapidly than the flow of air; consequently, to obtain the desired 









CARBURETERS 


21 


mixture, it is necessary either to reduce the suction, by per¬ 
mitting additional air to enter between the nozzle and the 
engine, or else to alter the rate of flow of the gasoline. By 
proper loading of the valve or valves controlling the auxiliary 
air supply, the suction exerted at the gasoline nozzle may be 
kept very close to that required to produce a uniform mixture 
at all speeds. The size of the orifice in the tip of the gasoline 
nozzle bears a definite relation to the size of the Venturi tube 
at its throat, and these proportions are determined by the 
designer. If, through imperfect fitting of parts and unskilful 


Fig. 14 

workmanship, there are air leaks in the engine, the nozzle 
orifice will need to be somewhat larger. 

34. A Venturi-tube type of gasoline carbureter for sta¬ 
tionary engines is shown in Fig. 14, (a) being a perspective 
and ( b ) a sectional view. The carbureter is bolted directly to 
the cylinder inlet by the flange a, and the air supply is drawn in 
through the horn b, which may be covered with a screen to 
prevent the entrance of dirt and grit. The gasoline spray 
nozzle c is central in the Venturi tube and the flow of gasoline 
is regulated by the needle valve d. The supply of fuel is kept 

















22 


CARBURETERS 


in a tank formed in the base of the engine and is drawn up by 
suction through a pipe connected at e. A ball check-valve in 
this pipe serves to keep the level constant in the spray nozzle. 
Surrounding the nozzle is a sleeve / that may be moved up or 
down by the handle g. When the engine is to be started, and a 
rich mixture is desired, the sleeve f is drawn up, thus partly 
closing the throat h of the Venturi tube. The flow of air is 
thus restricted and the suction exerted on the gasoline causes a 
heavy spray of it to be drawn into the mixing tube. 

35. A form of carbureter used on stationary gasoline 
engines is shown in Fig. 15, ( a ) being an outside view and ( b ) 
a section. Corresponding parts in both views are marked with 
the same reference letter. The gasoline enters at a and the air 
at b, so that the air flows downwards past the spray nozzle, 
instead of upwards as is more usual, and passes through the 
throttle valve and out at c. The float d is shaped so that it 
goes on each side of the mixing chamber. It is secured to a 
lever pivoted at the right, and in rising closes the regulating 
valve e. In the passage b is an automatic air-inlet valve f, 
closed by means of a spring g, as shown. This valve does not 
entirely close the air passage when it rests against its seat, but 
at the bottom is left an opening through which is supplied the 
necessary air for keeping the engine in operation under the 
slowest running conditions. As the suction increases, this 
valve opens against the spring g, thereby admitting a larger 
quantity of air. 

36. The gasoline passes directly from the float chamber to 
the spray nozzle h, Fig. 15, the opening of which may be reg¬ 
ulated by the needle valve i. As the opening of this nozzle is 
exactly in the center of the float chamber, the carbureter is not 
affected by being tilted. The throttle valve j is opened and 
closed by means of the lever k ; the mixture of air and gaso¬ 
line passes through in the direction indicated by the arrow. 
Adjustment of the automatic air valve f is obtained by modi¬ 
fying the tension of the spring g, by screwing up or unscrew¬ 
ing the shouldered stem l, which extends through the valve f to 
guide it, but is not attached to it. A drain cock m is provided 



23 


Fig. 15 



































































































































































24 


CARBURETERS 


at the bottom of the float chamber, for the purpose of emptying 
it or for drawing off water that may have got into it. 

37. A stationary gasoline engine usually runs at a nearly 
uniform speed, and therefore the carbureter or vaporizer is 
more easily adjusted to the running conditions than is the case 
with an automobile carbureter, which must give a fairly uni¬ 
form mixture over a wide range of speeds. To obtain the 
adjustment for the most economical use of fuel, the engine 
should be run at its usual speed under the load that it is to 
carry regularly. Then the needle valve that controls the flow 
of gasoline to the spray nozzle should be closed, a little at a 
time, until a point is reached at which further closing will 
reduce the speed and the power of the engine. At this point 
the amount of fuel supplied through the spray nozzle is just 
enough to keep the engine in motion at the desired speed and 
doing the required work. The carbureter will then be adjusted 
for economical service under those particular conditions of 
speed and load. If the load or the speed is altered, the engine 
will probably continue to run, but not necessarily with the same 
economy. 


CARBURETERS FOR AUTOMOBILE AND AEROPLANE ENGINES 

38. The greatest problem in connection with the carbura- 
tion of liquid fuel for use in automobile engines is to obtain a 
carbureter that will give a uniform mixture at all speeds. A 
float-feed carbureter of the elementary form shown in Fig. 2 
cannot do this, because the flow of fuel from the nozzle 
increases at a greater rate than the flow of air through the air 
tube when the engine is speeded up. In other words, if the 
ratio of fuel vapor to air is correct at a low engine speed, it 
will be too large at a higher speed, or, as it is commonly 
expressed, the mixture becomes too rich. This is just the 
opposite of the way the mixture should be; it will be most sat¬ 
isfactory if it is a little rich at very low engine speeds and 
becomes less rich as the engine speed increases. 

39. This statement about a carbureter of the elementary 
form shown in Fig. 2 must not be taken to mean that it is 



CARBURETERS 


25 


impossible to use a form so simple; its true meaning is that it 
will furnish a mixture substantially correct over only a rather 
narrow range of engine speeds and throttle openings. Thus, if 
the nozzle and the air tube are correctly proportioned for an 
engine speed of 400 revolutions per minute, the carbureter will 
probably deliver a substantially correct, although theoretically 
incorrect, mixture anywhere between perhaps 250 and 500 revo¬ 
lutions per minute. 

The quantity of mixture flowing from the carbureter to the 
engine is governed by a hand-operated throttle valve, which is 
usually made a part of the carbureter. Opening this valve 
allows more mixture to flow to the engine, which then increases 
its speed or power; and closing the throttle valve cuts down the 
quantity of mixture flowing to the engine and hence slows it 
down or decreases its power. 

40 . A carbureter that controls the mixture over only a very 
small speed and throttle-opening range is said to lack flexibility; 
and a carbureter controlling the mixture properly over a very 
large speed and throttle-opening range is said to be very 
flexible. Flexibility in a carbureter can be secured only by pro¬ 
viding means of compensating for the more rapidly increasing 
flow of the fuel over that of the air as the engine speed or 
throttle opening increases. A carbureter provided with such 
means is called a compensating carbureter, and if the means 
adopted work without the attention of the operator, it becomes 
an automatic compensating carbureter. 

41 . The carbureter shown in Fig. 15 is an automatic com¬ 
pensating carbureter, because it automatically adjusts the air 
supply to an increased flow of gasoline. It does this through 
the automatic air valve f. After the carbureter has been set 
and connected to the fuel supply and to the engine, it should 
be adjusted, first for low speed and then for high speed. The 
air valve is seated firmly but lightly by screwing down the 
knurled screw l, and the needle i is screwed shut and then 
opened about three-fourths of a turn. The carbureter is then 
ready for low-speed adjustment. The spark should be retarded 
and the throttle opened about one-fourth. The gasoline should 


26 


CARBURETERS 




then be turned on and 
the engine started, after 
which the needle valve 
should be opened until 
a point is reached at 
which the engine will 
run smoothly without 
missing explosions. 
The stop-screw on the 
throttle should be set 
so that the throttle 
cannot be closed com¬ 
pletely. The carbureter 
is then adjusted for 
low-speed running. 

42. To adjust the 
carbureter shown in 
Fig. 15 for the high 
speed of an automobile 
engine, the throttle k 
should be opened wide 
and the spark should 
be advanced about one- 
fourth. If the engine 
does not run smoothly, 
but backfires, the fault 
is due to the fact that 
the air valve / lifts too 
easily and admits too 
much air. The screw l 
should therefore be 
turned right-handed to 
increase the pressure 
of the spring g. If the 
engine continues to fire 
irregularly after the 
screw / has been given 






































































CARBURETERS 


27 


two full turns, the needle valve i should be opened a very 
slight amount more, to feed more gasoline. After these adjust¬ 
ments have been made, the screw / should be held by turning 
down the locknut against the body of the carbureter. The 
adjustment of the needle i can be locked by screwing up tightly 
the packing nut through which the needle passes into the bowl 
of the carbureter. 

43. An outside view and a sectional view of another form 
of carbureter are shown in Fig. 16 (a) and ( b ), respectively, 
corresponding parts in both views being lettered alike. The 
float chamber a forms the body of the carbureter and the 
needle valve b is centrally located in it. The needle valve has 
a seat in the casting c, in the side of which is a slot d leading 
to the annular chamber e. The chamber e is connected with 
the upper part of the float chamber by a small passage /. In 
the upper end of the casting c is formed a cup g into which 
dips the lower end of the tube h. The upper end of this tube is 
led into a chamber i that communicates, through a hole in the 
plug j, with the space k above the throttle valve /. The mix¬ 
ing chamber m is so formed that the air must pass from the 
inlet n down under the lower edge o. The float p is ring- 
shaped and controls the valve q through which gasoline is 
admitted by way of the connection r. The cock 5 allows the 
float chamber to be drained, and the vent t shown in (a) 
admits air to the upper part of this chamber. 

44. The carbureter illustrated in Fig. 16 has no air valves, 
and all of the air admitted must pass the spray nozzle. The 
gasoline level in the float chamber a is constant, and from this 
chamber the gasoline passes through the small opening u into 
the chamber e. It then flows through the slot d and rises past 
the needle valve b into the cup g, in which it stands at the same 
level as in the float chamber. When it is desired to start the 
engine, the throttle valve is opened very slightly, until it 
occupies the position shown. Then, on cranking the engine, a 
strong suction is exerted through the hole in the plug j and 
through the tube h, causing the small supply of gasoline in the 
cup g to be drawn up and sprayed into the intake manifold, 


28 


CARBURETERS 


and furnishing the desired rich mixture. This action is bound 
to take place, no matter what may be the condition of the 
weather. The cup g is quickly emptied at starting, and the 
gasoline is afterwards supplied from the chamber e through 
the orifice surrounding the tip of the needle valve. 

45 . The flow of gasoline from the float chamber a, Fig. 16, 
to the spray nozzle is limited by the size of the opening a, 
which is made large enough to supply enough gasoline for 
normal running. As the speed of the engine increases, the 
suction increases, and the level of the gasoline in the chamber e 
falls, because the flow through the orifice u is restricted. The 
distance through which the gasoline must be lifted is thus 
made greater, and the amount of gasoline issuing from the 
spray nozzle is decreased. If the speed increases still further, 
the level of the gasoline in the chamber e is lowered to such an 
extent that the slot d is partly uncovered. As soon as this 
occurs, air is drawn from the top of the float chamber through 
the pipe / and the slot d , and this stream of air reduces the 
suction around the needle valve. As a result, less gasoline is 
drawn up, and the mixture is maintained practically uniform. 
If it were not for this auxiliary stream of air, too much gaso¬ 
line would be drawn up at the higher speeds. The air supply 
to this carbureter should be preheated, by passing it over the 
exhaust pipe, if the best results are desired. 

46 . The carbureter shown in Fig. 16 has only one adjust¬ 
ment, which is made by turning the milled head fastened to the 
needle valve b. After the engine is started, the regulating 
sleeve on the hot-air pipe should be turned so as to supply a 
mixture of equal parts of hot and cold air. The engine should 
be allowed to run until the intake manifold gets warm. Then 
the throttle control lever on the steering wheel should be 
opened about one-eighth of its throw, and the gasoline needle 
valve b should be screwed in until the engine begins to misfire, 
due to lack of gasoline. The valve b should then be screwed 
out slowly, which gradually increases the supply of fuel, until 
the point is reached at which the engine picks up speed and runs 


CARBURETERS 


29 


regularly without misfiring. The carbureter is then correctly 
adjusted. 

47. Some makes of carbureters are fitted with com¬ 
pensating jets to regulate the flow of gasoline for varying 
speeds. Fig. 17 shows a carbureter of this type. It has a 
compound nozzle, which is really made up of two nozzles, one 
within the other. A main nozzle or jet a of the usual form is 
surrounded by an 
outer tube or cap jet b. 

The supply of gaso¬ 
line for this outer jet 
passes through the 
small opening c and is 
limited to the amount 
that can flow through 
that opening, which is 
known as the compen¬ 
sating jet. Air from 
outside of the carbu¬ 
reter is allowed to en¬ 
ter freely through two 
holes, one of which is 
shown by the dotted 
circle d, which admit 
air freely to the well e, 
and through the pas¬ 
sage /. This free 
passage of air pre¬ 
vents any great in¬ 
crease of suction on the jet c when the speed of the engine 
increases, and therefore gasoline flows through the jet c at 
approximately the same rate when the engine is running at 
2,000 revolutions per minute as when running at 500 revolu¬ 
tions per minute. This part of the nozzle therefore produces 
a much weaker, or leaner, fuel mixture at the higher speed 
than at the lower speed, thus balancing, or compensating, the 
increased flow of gasoline from the inner jet a at the higher 



Fig. 17 












































30 


CARBURETERS 


engine speeds. This is due to the fact that the suction on the 
inner jet a increases as the engine speed increases, owing to the 
higher velocity of the air past the nozzle, whereas the suction 
on the compensating jet c does not increase as the engine speed 
increases. It will be seen that by selecting the correct sizes for 
both jets an adjustment can be made that will give an approxi¬ 
mately correct fuel mixture at all of the varying working speeds 
of the engine. 

48. The flow of gasoline at the idling speed or slow speed 
without load is controlled by the idling device, consisting of a 
tube g, called the idling well, or secondary well, which is 
screwed into the body of the carbureter at h, and a small inner 
tube i, called the primary tube, to conduct the fuel to the pas¬ 
sage k. The richness of the mixture is limited by the amount 
of gasoline that can flow through the small hole or jet /, and is 
regulated by the adjusting screw m, which admits more or less 
air. 

The idling device operates only when the throttle o is nearly 
closed, or when the engine is running at idling speed. The suc¬ 
tion is then very strong at the point k and very slight on the 
nozzle a b. The adjusting screw m has, however, only a 
limited effect, and when considerable change of speed is needed, 
the outer tube, or secondary well, g is removed by unscrewing 
the tube and substituting a tube having a smaller or larger jet l. 
Some carbureters do not have the secondary well g, but limit 
the fuel supply by restricting the passage in the tube i, the air 
in this case being measured, or regulated, entirely by the regu¬ 
lating screw m. Turning this screw out admits more air past 
the screw and reduces the suction on the tube i so that it draws 
less gasoline and makes the mixture leaner; screwing it in gives 
a richer mixture. 

49. The idling wells g and e, Fig. 17, fill with gasoline to 
the level of the gasoline in the float chamber as soon as the 
suction is stopped. Then, when the engine is cranked with the 
throttle nearly closed, or set for idling speed, the suction is 
greatest at the edge of the throttle and draws gasoline from 
the idling device instead of from the main nozzles, and delivers 


CARBURETERS 


81 


a rich mixture until the supply of gasoline in the secondary 
well g is exhausted. It will then deliver the regular idling- 
speed mixture so long as the throttle remains at the position for 
idling speed. As the throttle is gradually opened, the suction 
on the idling device is lessened and the suction at the mouth of 
the nozzles a and b is increased until the point is reached where 
the fuel comes entirely from the nozzles a and b and no fuel is 
then delivered through the idling device. The outer well e 
remains filled with gasoline while the engine is running at idling 
speed, but if the thyottle is opened suddenly a very rich mixture 
is delivered from the jet b during the first few turns of the 
engine and until the supply of gasoline in the well e is 
exhausted, thus furnishing the desired rich mixture which the 
increasing speed of the engine requires. If the throttle is 
opened gradually, the supply of gasoline in the well e is 
gradually diminished and when exhausted the part b of the 
nozzle can deliver only the amount of gasoline that can flow 
through the jet c. 

50. If the main jet a is too small, the mixture will be too 
lean when the engine is running at high speed. If it is too 
large, it will give too rich a mixture at high speed. The jet a 
may thus be thought of as the high-speed adjustment, because 
the flow of gasoline through it is most affected when the suction 
of air through the Venturi tube, or choke tube, v is strongest, 
as it will be when the engine is running at high speed. Simi¬ 
larly, the compensating jet c may be thought of as the adjust¬ 
ment for loaded slow speed, or slow speed when the throttle is 
open, as it will be when the engine is making a hard pull. If 
the engine is running slow without load, the throttle will have 
to be nearly closed, which will bring into use the idling device, 
as previously explained. If the choke tube v is too large, the 
gasoline will not be fully vaporized, owing to the low velocity 
of the air, which will result in particles of raw fuel being drawn 
into the engine and making a slow burning mixture; the 
engine will also not respond quickly when the throttle is opened. 
If the choke tube v is too small, the passage of air will be 
restricted, with an effect similar to that when the throttle is 

356-9 


32 


CARBURETERS 


paitly closed, and the engine will be prevented from developing 
its full rated power. 

51. These four adjustments, or variables , as they are called, 
the choke tube v, main jet a, compensating jet c, and idling jet l, 
seldom need changing after the carbureter is once fitted to an 
engine. Their sizes are designated by the diameters of the 
holes through them. The size of the choke tube is indicated in 
millimeters at the throat diameter, or smallest part of the inside 
diameter, and the jets are marked in hundredths of a milli¬ 
meter. A compensating jet marked 150 would mean that the 
hole in the jet has a diameter of 150 hundredths of a milli¬ 
meter, or one and one-half millimeters. 

52. Some carbureters compensate for different engine 
speeds by means of what are called air-hied jets , which have 

been proved experimentally 
when properly constructed to 
give a constant proportion ot 
gasoline and air at all speeds. 
The principle of construction of 
the air-bled jet is shown in 
Fig. 18. Placed in the center of 
the usual Venturi tube a, called 
in some carbureters the choke 
tube, through which the air 
passes at high velocity, is a 
second but smaller Venturi tube b the mouth of which is at 
the throat of the tube a. Eight very small holes c are drilled 
through the wall of the tube h slightly above its throat; it 
will be understood that, owing to the two Venturi tubes being 
in series, a very high air velocity is obtained under the suc¬ 
tion of the engine at the throat of the Venturi tube h, even 
at fairly low engine speeds, which greatly aids the atomization 
of any fuel leaving the jet holes c. These holes c commu¬ 
nicate with a passage d leading to the float chamber of the 
carbureter; this passage d, through holes e drilled into its wall, 
communicates with the air by way of the passage / and holes in 
the cap g.< With the engine running, liquid fuel is forced by 






















CARBURETERS 


33 


atmospheric pressure, due to the vacuum in the two Venturi 
tubes a and b, up the passage d to the holes e, where air enters 
and mixes with the liquid gasoline, changing it to a finely 
divided emulsion, or froth, which emulsion passes through the 
jets c into the Venturi tube b, where it is further atomized and 
diluted by the air passing through b at high velocity. The 
finely divided mixture of gasoline vapor and air, leaving the 
mouth of the tube b at the throat of the Venturi tube a, passes 



the throttle valve (not shown) and goes to the engine cylinders. 
As in all carbureters, changing of the liquid gasoline globules 
into vapor is effected not only by atomization but also by 
vaporization, which is assisted by preheating the air admitted 
through the Venturi tubes. 

To sum up, an air-bled jet, instead of passing liquid gasoline 
into the mixing chamber, supplies an emulsion consisting of 
very small globules of gasoline suspended in air. 


























































34 


CARBURETERS 


53. The general construction of one make of carbureter 
using an air-bled jet is shown diagrammatically in Fig. 19. 
The gasoline enters at a and passes into the float chamber b, 
whence it passes through an orifice at c fitted with an adjust¬ 
able needle valve d into the passage d'. At the end of this 
passage is a plug having a central hole and an annular cham¬ 
ber e called the accelerating well; the so-called idling tube f 
passes through the central hole of the accelerating well. The 
idling tube / receives gasoline through the small hole g. The 
accelerating well has three small holes drilled through its inner 
wall, a vent hole drilled through its upper end, and several small 
holes drilled through its lower end to communicate with the 
gasoline chamber h to which the fuel is supplied by the needle 
valve at c. The passage containing the idling tube / terminates 
at a plug i located above the throttle j when the throttle is in its 
closed position. The small Venturi tube is shown at k, and the 
large one at l; both Venturi tubes receive preheated air through 
the air tube m provided with a strangling valve n for enriching 
the mixture when starting the engine in cold weather, by 
throttling the air supply. The liquid gasoline for the emulsion 
of gasoline and air supplied to the small Venturi tube k is 
drawn from the chamber h through the annular opening 
between the idling tube / and the hole in the plug containing 
the accelerating well e. The air-admission plug o supplies the 
air for the air-bled jets in the Venturi tube k ; an air opening 
at p fitted with a low-speed needle valve q supplies air to the 
gasoline passing out through the idling, or low-speed, plug i. 

54. The operation of the carbureter illustrated diagram¬ 
matically by Fig. 19 is as follows: When idling, the throttle j 
is closed. Under this condition, gasoline is drawn from the 
chamber h, through the idling tube /, and mixes with air 
admitted through the passage p, the combustible mixture pass¬ 
ing through the idling plug i into the space above the throttle 
and thence to the engine. When idling, the two Venturi 
tubes k, l and the air-bled jets are out of action, and just 
enough air passes, at a very low velocity, through the Venturi 
tubes to supply that required for the idling mixture. 


CARBURETERS 


35 


When the engine is speeded up through opening the throttle j 
slightly, the vacuum in the intake manifold of the engine is 
increased, and therefore the air-bled jets come into action; for 
very low throttle positions the mixture is fed to the intake by 
both the idling jet i and the air-bled jets. As the throttle is 
still further opened, the gasoline is drawn faster from the 
idling tube f than it can enter through the hole g, and conse¬ 
quently the idling jet automatically goes out of action, all the 
fuel now being supplied by the air-bled jets in the smaller 
Venturi tube k. It will be plain that the annular opening at c 
should be just large enough to keep the chamber h filled with 
gasoline at all motor speeds; this opening is regulated by trial 
by screwing the adjusting screw d up to strengthen the mixture 
and down to weaken it. The strength of the mixture for idling 
is adjusted by trial by means of the low-speed adjusting 
screw q, the throttle being fully closed. 

55 . It is a well-known fact that a carbureter set for a weak 
mixture, which means an economical mixture, will fail to give 
good acceleration, that is, will not permit quick throttle open¬ 
ing and consequent quick response of the car. Quick accelera¬ 
tion can be secured in two ways, which are by a permanent 
setting of the carbureter for a rich and hence very uneconom¬ 
ical mixture, or by temporarily enriching the mixture during 
acceleration and then returning to the former economical 
setting. The latter alternative is employed in the carbureter 
illustrated in Fig. 19, the accelerating well serving the pur¬ 
pose of temporarily enriching the mixture and automatically 
returning to an economical mixture after acceleration. 

56 . With the engine running at a constant speed corre¬ 
sponding to a car speed of about 20 miles per hour, the accel¬ 
erating well e, Fig. 19, is filled with gasoline to the top. But, 
if the engine speed is now increased suddenly, the gasoline is 
drawn faster from the chamber h than it can flow into it past 
the orifice c, and there would quickly exist a deficiency of fuel 
in the chamber h, were it not that the accelerating well e dis¬ 
charges the fuel it holds, through the holes in its bottom head, 
into the chamber h, thereby temporarily doubling the normal 


36 


CARBURETERS 


rate of gasoline flow into the chamber li and thus supplying 
the fuel needed for acceleration. By the time the car has 
speeded up, sufficient fuel flows through the orifice c to supply 
the chamber h with all the fuel needed. When the car slows 
down, the accelerating well gradually fills again with gasoline 
and is ready for the next sudden acceleration. 

57. To adjust the carbureter shown in Fig. 19 for idling, 
the engine is started with the low-speed adjustment screw q 
approximately one-half turn off its seat. When the engine has 
warmed up, the screw q is turned out, that is, counter-clock¬ 
wise, until the engine idles steadily. As a general rule, the 



device is properly adjusted when the screw q is somewhere 
between one-half and one and one-half turns off its seat. The 
adjusting screw d adjusts the mixture over the whole driving 
range. An approximate adjustment is obtained by turning it 
about three whole turns off its seat, which will probably give a 
rather rich mixture, and then screwing it in until trial shows a 
sufficiently weak mixture. 

58. A carbureter made with an auxiliary air valve is 
shown in section in Fig. 20. The gasoline enters at a and is 
maintained at a constant level in the glass float chamber b by a 
metallic float c and needje valve d. The low-speed spray 



















































CARBURETERS 


37 


nozzle e terminates at the throat of the Venturi tube /; the 
high-speed nozzle g opens into the mixing chamber. The 
auxiliary air valve h has below it the low-speed spring i, 
the tension of which can be adjusted by means of the low-speed 
adjusting nut /. The high-speed spring k is placed above the 
auxiliary air valve h and serves to limit the distance this valve 
can open, the high-speed adjusting nut l being used to regulate 
this distance. With the engine at rest, there is on an average 
a clearance of iV inch between the top of the high-speed 
spring k and the bottom of the air-valve cap nut m. A. 
strangling valve n is placed in the main air intake o, which 
valve carries a cam p so adjusted that it will lock the air valve h 
to its seat when the strangling valve is closed. This permits 
an exceedingly rich mixture to be drawn into the cylinders 
when starting a cold engine. A flexible metallic tube leading to 
a heater is usually attached to the main air intake o. 

59 . The carbureter shown in Fig. 20 has no gasoline 
adjustments, the correct size nozzles being fitted at the factory. 
The method of adjusting the carbureter is as follows: With 
the engine at rest the low-speed nut j is turned until the air 
valve h seats lightly; then the high-speed nut l is set until there is 
about inch clearance between the spring k and the cap nut m. 
The engine is now started and run until thoroughly warmed up; 
then, with the engine idling, the low-speed nut j is turned right- 
handed until the engine slows down and then is turned left- 
handed about three notches, or until the engine runs strongly 
again. The throttle is now opened gradually and the spark 
advanced to the usual running position. If the engine back¬ 
fires into the carbureter, the high-speed nut is turned left- 
handed until all back-firing stops. If the engine fails to 
respond promptly to the opening of the throttle, it shows the 
mixture is slightly weak; this can be corrected by turning both 
adjusting nuts left-handed one or two notches. The idling 
speed is adjusted by means of the usual throttle stop-screw. 

60. Another make of carbureter is shown in section in 
Fig. 21 (a) and in perspective in ( b ) ; the same parts are 
lettered alike in both views. The fuel enters the carbureter 


38 


CARBURETERS 


at a and passes through a removable wire-gauze screen b into 
the float chamber, in which the float c and needle valve d main¬ 
tain a constant gasoline level. The lower end of the fixed 
primary spray nozzle e is submerged in the gasoline. A tube / 




(b) 

Fig. 21 


carries the gasoline to the dashpot chamber g, and by way of 
the passage h to the secondary gasoline nozzle i, which has a 
variable annular opening the size of which is governed by the 
metering pin /. This metering pin moves up or down with the 


















































































CARBURETERS 


39 


auxiliary air valve k, the lower end of which carries a piston l 
that is a loose fit in the dashpot chamber g. A passage m opens 
the top of the dashpot chamber to the atmosphere, so that the 
gasoline can flow freely into this chamber and keep it filled. 

61. The air valve k, Fig. 21, is held to its seat by the helical 
spring n, the tension of which is correctly adjusted at the fac¬ 
tory. An arm o is rigidly fastened to the auxiliary air valve 
and by means of a link p is attached to the butterfly valve q, 
which in the position shown closes the lower air entrance to the 
mixing chamber r, at the top of which the butterfly throttle 
valve ^ is located. The opening in the primary spray nozzle e 
is varied by means of the needle valve t, which is interconnected 
to the throttle valve in such a manner that opening the throttle 
raises the needle valve against the resistance of the spring t'. 
A constant air opening into the mixing chamber is drilled 
through the side of the carbureter, as shown at u. The valve t 
is raised or lowered by an arm of the shaft v, which arm enters 
a slot cut into the side of the valve t. This shaft v passes 
through a bearing formed on the body of the carbureter, and 
to its outer end is pinned a bracket ?/. Mounted loosely on the 
shaft v is a bell-crank whose arms are indicated by w and ze/. 
The arm w carries the low-speed adjusting screw x that bears 
against a cam x f on the lower end of a vertical shaft that may 
be rotated in the bracket if by means of the lever x" and dash 
adjustment wire x t . The arm istf of the bell-crank carries a 
steel tongue w 1 that bears against the curved surface of a steel 
block y, the position of which in reference to the throttle-valve 
shaft can be slightly changed by means of the high-speed 
adjustment screw z . 

62 . With the engine at rest, the two auxiliary air inlets are 
closed. To start the engine, the wire x 19 Fig. 21, is pulled out, 
which turns the cam x f and thereby lifts the needle valve t from 
the nozzle e, thus setting the carbureter temporarily for a rich 
mixture suitable for starting. If necessary, the carbureter is 
primed as well by pulling on the priming lever c', which per¬ 
mits gasoline to overflow from the primary nozzle e into the 
mixing chamber. After the engine fires and as soon as it has 


40 


CARBURETERS 


warmed up, running idly, the wire x x is pushed in, thereby 
dropping the needle valve t and thus setting the carbureter for 
a leaner mixture. At idling speeds, practically all air for the 
combustible mixture is drawn through the constant air open¬ 
ing u, but at the higher engine speeds the two auxiliary air 
valves open in proportion to the engine speed. The opening of 
the throttle lifts the needle valve t, thereby increasing the gaso¬ 
line supply from the nozzle e ; the opening of the auxiliary air 
valve k pushes the tapered metering pin j down, thereby open¬ 
ing the secondary gasoline nozzle i. The two nozzles and other 
parts are so proportioned as to maintain a practically constant 
ratio of gasoline to air at all engine speeds. 

The dashpot piston /, by offering a fixed resistance to the 
motion of the air valve k in either direction, prevents any 
fluttering of the air valve, and thereby promotes a more 
thorough and uniform mixture of the gasoline and air in the 
mixing chamber. The small tube t x assists in getting a rich 
mixture above the throttle when the engine is idling. 

63. The carbureter shown in Fig. 21 has only a low-speed 
and a high-speed gasoline adjustment; in adjusting this car¬ 
bureter it is well to remember that turning the adjusting screws 
to the right enriches the mixture and turning them to the left 
weakens the mixture. Also, the low-speed adjustment must 
be completed before the high-speed adjustment is attempted; 
the engine should be properly warmed up, and the dash control 
set for the weakest mixture. 

To make the low-speed adjustment, with the throttle closed 
and the dash control down, the low-speed adjustment screw x 
is turned slowly to the left until the steel tongue w x is just 
out of contact with the high-speed cam y ; the screw x is then 
turned to the right about three complete turns. The throttle is 
now opened slightly, the carbureter is primed by means of the 
priming lever c', and the engine is started and allowed to run 
until thoroughly warmed up. The throttle is then closed until 
with a slightly retarded spark the engine runs slowly; the low- 
speed adjusting screw x is then turned slowly to the left until 
the engine slows down a little, and is then turned to the right, 


CARBURETERS 


41 


a notch at a time, until the engine idles smoothly. The idling 
speed is controlled by a throttle-arm stop-screw, which cannot 
be seen in the illustration, and which is turned to the left to 
lower the idling speed. 

To make the high-speed adjustment, the spark is advanced 
somewhat and the throttle is quickly opened. If the engine 
back-fires into the carbureter when speeded up, it shows that 
the mixture is too weak at high speeds, and must be enriched 
by turning the high-speed adjusting screw z to the right, one 
notch at a time, until there is no sign of back-firing when the 
throttle is opened quickly. If the engine chokes when the 
throttle is opened, it indicates too rich a mixture, and the high¬ 
speed adjusting screw should be 
turned to the left until the engine 
begins to back-fire, and then to 
the right again until it runs satis¬ 
factorily at high speeds. 

64 . Aeroplane engines nearly 
always use a carbureter of the 
compensating-jet type and usu¬ 
ally made of aluminum to insure 
lightness. An outside view of 
an aeroplane carburetef is shown 
in Fig. 22 and a view of the same 
carbureter partly in section is 
shown in Fig. 23, the reference 
letters being the same as in 
Fig. 17, so far as they apply. It 
has a single float chamber z, but 
is otherwise like two separate carbureters. Each side is com¬ 
plete in every respect, with its own choke tube v, throttle o, 
compound nozzle a b , compensating jet c, and well e. Each side 
has its own idling device and each side supplies its own set of 
cylinders. The operation of this carbureter is the same as that 
of the carbureter shown in Fig. 17 and explained in Arts. 47 
to 51 , except that this one has no adjusting screw for the 
idling device, the adjustment of the idling speed being made by 














42 


CARBURETERS 


changing the inner idling well g for one with a larger or smaller 
jet / as may be needed, thus eliminating the risk of the adjust¬ 
ment changing while the engine is in the air. In the large 
twelve- or sixteen-cylinder engines, two double, or duplex, 
carbureters are generally used, so that each half of each car¬ 
bureter supplies only three or four cylinders of the engine, the 



object being to secure a uniform charge in all cylinders and 
prevent vibration of the engine, and also to secure a higher 
velocity of air through the Venturi tubes than could be secured 
with one carbureter having a Venturi tube of very large pro¬ 
portions This high velocity of air past the nozzle helps to 
vaporize the fuel more fully. The throttles all operate 
simultaneously. The shafts on which the throttles are mounted 































CARBURETERS 


43 


are parallel to each other and are connected together in each 
carbureter by segments of a gear, one of which is shown at p. 
The shafts between the carbureters are connected by couplings, 
one of which is shown at q. The detachable bottom or air 
intake r is held in place by two springs, one of which is shown 
in Fig. 22. A small drain pipe to carry off any accidental over¬ 
flow of gasoline is connected at s. 

65 . In the high altitudes reached by airplanes the air is 
lighter than it is near the ground and the engine requires less 
gasoline to keep the fuel mixture of the correct proportions. 
The ordinary carbureter will supply about the same amount of 
gasoline in the light air as it does in the heavier air, which 
makes too rich a mixture in the high altitudes; an additional 
adjustment is therefore needed. The altitude adjustment 
device shown in Fig. 23 secures this result by lessening the 
supply of gasoline. It consists of a hollow shaft t in which are 
ports u open to the suction of the engine at a point just above 
the Venturi tube v, where the suction is strongest. Connection 
is thus made through the passage w, port w, hollow shaft t, and 
passage x to the float chamber z. The shaft t is fastened to the 
lever y, which is operated by hand by connections placed within 
reach of the pilot. When this lever y is moved, it rotates the 
hollow shaft t and operates in a manner similar to the opening 
or closing of an ordinary petcock. The pilot opens this a little 
at an altitude of 2,000 or 3,000 feet, and as he rises he opens it 
more. When this device is open, a passage for air is made from 
the float chamber z through the passage x, hollow shaft t in 
both directions, and through the passages w to the Venturi 
tubes v, one of these passages w and one of the Venturi tubes 
being shown in Fig. 23. This allows the suction of the engine 
to create a partial vacuum in the float chamber z because the 
float chamber is air-tight except for some very small holes that 
are open to the atmosphere. This partial vacuum in the float 
chamber has the effect of lowering the pressure on the gasoline 
in the float chamber and consequently less gasoline will flow 
from the main jet a, thus giving the desired weaker mixture 
which the lighter air requires. 


44 


CARBURETERS 


CARBURETERS FOR TRACTORS 

06, The carbureters used on gasoline and kerosene trac¬ 
tors do not differ in principle from those used on stationary 
and automobile engines; but the conditions of tractor service 
differ considerably from the conditions that exist in the run¬ 
ning of automobile engines. The speed of a tractor is ordi¬ 
narily between 1J and 4 miles per hour, and the speed range of 
the engine is small as compared with that of an automobile 
engine. The adjustment of a carbureter on a tractor is there¬ 
fore a simpler matter than the corresponding operation on an 
automobile. The engine of a tractor runs at a fairly constant 
speed, this object being accomplished by means of a governor 
attached to the crank-shaft or the cam-shaft or driven by gear¬ 
ing from some rotating part. The governor is connected by 
rods and levers to a swinging throttle or butterfly valve in the 
pipe leading from the carbureter to the intake of the engine. If 
the speed increases, the governor balls or weights move out¬ 
wards and their movement is transmitted to the butterfly valve, 
closing it somewhat and thus decreasing the amount of fuel 
supplied to the engine. The engine then develops less power 
and the speed is reduced to the normal. If the speed decreases, 
the action of the governor opens the butterfly valve farther, 
increases the fuel supply and the power, and brings the speed 
back to the normal. A lever from the throttle valve to the 
driver’s platform enables the operator to vary the speed at will. 

67 . The carbureters of many tractors are designed to 
handle economically the various grades and qualities of liquid 
fuel, including gasoline, naphtha, kerosene, and distillate. 
This arrangement is advantageous, in that it permits the use of 
the class of fuel that is cheapest or most readily available in 
any particular neighborhood. In other cases, two carbureters 
are used. These are set side by side and are connected to the 
intake pipe leading to the engine by means of a three-way cock. 
One carbureter is adjusted to use gasoline and the other to use 
kerosene or some other low-grade fuel. The tractor is started 
on gasoline and brought to normal running condition. Then 


CARBURETERS 


45 


the three-way cock is thrown over quickly, cutting out the 

gasoline carbureter 
and bringing the 
kerosene carbureter 
into action. Water 
spray is injected 
with the kerosene 
through a suitable 
valve, in the manner 
already described. 
Many makes of trac¬ 
tors use standard 
carbureters, such as 
are commonly used 
in automobile prac¬ 
tice. 

G8. An enclosed 
pattern carbureter 
used on gas tractors 
--/qN—. is shown in perspec- 
—Itive in Fig. 24 (a) 
and in section in (b). 
The nozzle a is in 
the center of the 
Venturi tube b and 
is surrounded by the 
float chamber c. The 
flow of gasoline is 
regulated by a 
needle d that ex¬ 
tends beyond the top 
of the carbureter 
and is fitted with a 
winged head e. The 
main air supply en¬ 
ters at f, flows through the passage g, and rises around the 
nozzle a, passing thence into the mixing chamber h. The auxil- 








































































































46 


CARBURETERS 


iary air enters the mixing chamber by lifting one or more of the 
balls i from their seats. These balls all have the same diameter 
and hence the same weight. The mixture then passes the 
throttle valve j and enters the inlet manifold. Each ball i is of 
bronze and is held in a cage formed by the cap k. The tube 
forming the passage g is held in place on the central stem by 
means of the nut l, and the float chamber c may be turned in any 
desired direction. The screw m locks the needle d in position 
after the latter has been adjusted. 

69. The carbureter shown in Fig. 24 has but one adjust¬ 
ment, namely, that of the needle valve. When the needle d has 
once been set correctly at low speed, the correct explosive mix¬ 
ture at other speeds will be produced by the automatic action of 
the balls i. To adjust this carbureter, the head e of the needle d 
is first turned to the right until it will go no farther. The 
gasoline nozzle a will then be completely closed. The screw m 
should be loosened, so that the needle d may turn easily. The 
needle should now have one complete turn to the left, and the 
engine should be started. With the spark retarded, the throttle 
slightly open, and with the engine running, the needle d should 
be slowly turned to the right until the engine begins to back¬ 
fire ; then it should be turned slowly to the left until the engine 
runs at its maximum speed for that throttle opening, after 
which it should be locked in this position by tightening the 
screw m. 

70. Kerosene Carbureter.—The form of kerosene car¬ 
bureter used on the Ford tractor is shown in perspective in I 
Fig. 25 and in section in Fig. 26 (a) and (6). The intake 
manifold a and the exhaust manifold b are cast in one piece, j 
and between the exhaust manifoid and the pipe c leading to the 
muffler is formed a chamber d that contains the vaporizing 
coil e. This coil, made of light brass tubing, is connected at one 
end to the carbureter / and at the other end to the pipe g lead¬ 
ing to the main air valve h. The float chamber of the car- j 
bureter f is connected to the kerosene supply pipe at i. The j 
suction created by the engine draws the kerosene through the 
nozzle j and sprays it into the air that is drawn in through the 


CARBURETERS 


4T 


pipe k from an air washer. The mixture passes into the coil e, 
where it becomes heated by the exhaust gases surrounding the 
coil. The amount of heat is regulated by raising or lowering 
the sleeve valve l. In the position shown, the exhaust gases do 
not come in contact with the coil; but if the sleeve l is raised, a 
part of the exhaust will pass through the chamber d. By this 
arrangement, the heating of the vaporizing coil may be varied 
to suit the atmospheric conditions. The adjusting lever m of 
the valve / is provided with a notched sector at n. 



Fig. 25 


71 . The rich mixture of kerosene vapor and air passes up 
the pipe g, Fig. 26, and through the two-way valve o into the 
Venturi tube p, where it meets the air supply received through 
the main air valve h from the air washer. The mixture then 
passes down into the intake manifold a. When the engine is to 
be started, gasoline is used as the fuel. The gasoline pipe is 
connected at q, from which a passage leads into the body of 
the valve o. This passage is approximately at right angles to 
the one through which the kerosene vapor flows. Consequently, 
when the engine is to be started, the two-way valve is turned a 
quarter-turn from the position shown, which shuts off com¬ 
munication with the kerosene vaporizing coil and opens com- 


356—10 
































48 


Fig. 26 


































































































































































CARBURETERS 


49 


munication between the gasoline supply q and the Venturi 
tube p. When the engine has been started and is running 
smoothly, the two-way valve is swung back, and the engine 
takes up its normal operation on kerosene as fuel. Only about 
one-tenth of the air required is admitted through the pipe k, 
and the remaining nine-tenths is mixed with the rich mixture 
at the Venturi tube p. 



72. When only the lightest and most easily vaporized fuel 
is used, such as the highest grade of gasoline, little or no heat 
is needed to vaporize it, except in cold weather, and a simple 
mixing valve or simple carbureter could then be used, but 
when heavier fuel like kerosene is used, and especially the 
heavier grades of kerosene, more heat is required to vaporize 
it. A form of carbureter is shown in Fig. 27 which is designed 

























































50 


CARBURETERS 


to use a fuel which requires a temperature of 600 degrees F. to 
vaporize it fully. These lower grades of fuel, produced from 
the mineral oil called petroleum, are separated from the heavier 
oils by distilling; that is, heating the oil to the desired tempera¬ 
ture—in this case 600 degrees—and collecting whatever vapor 
is driven off. This vapor becomes a liquid as soon as cooled, 
but will become vapor again when the same amount of heat is 
applied to it. This is what the carbureter shown in Fig. 27 is 
designed to do; 600 degrees may therefore be said to be the 
vaporizing point, or boiling point, of this liquid. But, the 
petroleum from which it is made has probably been previously 
distilled at some lower heat, as, for instance, 300 degrees. Then 
this particular liquid, or distillate, would contain only that part 
of the petroleum which would vaporize between 300 degrees 
and 600 degrees, and could be considered as composed of 
ingredients having boiling points all the way from 300 degrees 
to 600 degrees, or, as it is sometimes spoken of, a low end point 
of 300 degrees and a high end point of 600 degrees. 

73 . In the carbureter shown in Fig. 27 the fuel enters at a 
and is maintained at a constant level in the float chamber b by 
the usual means. It enters the well c through holes d which 
may be more or less closed by screwing in or out the sleeve e, 
which is held by the spring /. A suction tube g is placed in the 
well and adjusted so the top is slightly above the top of the fuel 
in the float chamber. The fuel is drawn, by the suction of the 
engine, over the top of the suction tube down through the tube 
and out through the holes h, being partly broken into spray by a 
limited amount of air admitted through a small hole i near the 
top of the well c. 

The mixing chamber j is of unusual construction, in that the 
air enters at the side of the bowl, or tangentially, and is dis¬ 
charged at the bottom k, which gives the air a violent whirling 
motion about the suction outlets h, thus creating a partial 
vacuum in the center which causes the fuel to flow through the 
orifice h in exact proportion to the velocity of the air passing 
through the mixing chamber. This vacuum also helps greatly 
in breaking up the fuel into the desired fine particles, and, at the 


CARBURETERS 


51 


same time, the whirling and downward movement of the air and 
fuel tends to throw the heavier particles of fuel against the 
sides of the mixing chamber with considerable force. The 
lighter part of the fuel is in this way vaporized in the mixing 
chamber and passes on directly to the cylinders of the engine, 
but the heavier part of the fuel—that is, the part having the 
higher boiling point—is vaporized by the special heating appa¬ 
ratus contained in the bottom of the carbureter, which heats it 
to the vaporizing temperature, or boiling point, and the vapor 
goes to the engine in the form of gas before it has time to cool 
to the liquid state again. 

74 . That part of the fuel which does not vaporize in the 
mixing chamber will collect at the bottom of the carbureter and 
run through the fine screen l, where it strikes the hot plate m 
and is converted into vapor. The plate m is kept hot by the 
burning of some of the fuel in the chamber o. The fuel is kept 
on fire by the spark plug p. The mixture cannot become explo¬ 
sive, because air is not supplied in sufficient quantity. The 
cement cone q, made of material that stands high heat, protects 
the lower end of the tube or chimney r and also helps to heat 
the plate m. A ring q ' in the bottom of the combustion chamber 
is made of the same material as the cone q and acts as a wick 
which helps to keep the fire burning smoothly. 

A small wire s, placed loosely in the tube r, is shaken about 
by the natural vibration of the engine, and thus removes the 
soot that would otherwise collect in the tube; also, a small 
vent t, by admitting air, prevents the formation of soot on the 
spark plug p. A drain vent u prevents the combustion chamber 
from flooding, and a vent v admits a limited amount of fuel 
mixture from the mixture passage w to the chamber o. The 
fuel mixture passes over the top of the inside tube x in the cap y 
and down through the passage v. This vent regulates the heat 
or rate of vaporization at working speeds of the motor in the 
combustion chamber o, and is governed by the condition of the 
fuel mixture in the mixture passage w. When the mixture is 
rich, more fuel and less air will pass through v, which will 
retard the vaporization in the combustion chamber. If the fuel 


52 


CARBURETERS 


mixture in w is lean, it will cause more air to pass through v, 
which will increase the vaporization in the combustion chamber, 
thus automatically compensating for different fuel conditions 
and also different temperature conditions, because in cold 
weather less of the fuel is vaporized in the mixing chamber j, 
making a leaner mixture in the passage w. 

75. The flow of gasoline when starting, and at idling speed, 
is taken care of in the carbureter shown in Fig. 27 by means of 
the independent gasoline priming device z and the thermostat a,'. 
If the motor has been stopped but a few minutes it can be 
started on kerosene by flooding the carbureter in the usual way 
by pressing down on the priming pin b', which depresses the 
float. If the engine is cold, the start is made on gasoline by 
opening a hand-operated needle valve at z, similar to opening an 
ordinary petcock, and allowing gasoline to run through the 
opening c f into the chamber o where it is set on fire when the 
the engine is cranked, by the spark plug p, because the spark 
plug is connected in series with an insulated, or series, spark 
plug in one of the cylinders. This furnishes gasoline vapor to 
run the engine for the first few turns and also heats the com¬ 
bustion chamber so it will vaporize the regular kerosene fuel. 
The thermostat, or temperature regulator, a' operates by 
expansion of the diaphragm d' which, when hot, pushes forward 
the control plug e' which closes more or less the port /'. The 
upward draft of vapor is thus controlled through the tube r 
when the throttle is in the closed position, thus regulating the 
rate of vaporization in the chamber o while the engine is 
running at idling speed. 


FUEL SUPPLY 


METHODS OF SUPPLYING FUEL TO CARBURETERS 

76 . The tank that carries the fuel for an automobile may 
be located either at a level considerably higher than the car¬ 
bureter, so that the liquid will flow freely to the carbureter by 
gravity, or on the same or a lower level than the carbureter, so 




CARBURETERS 


53 


that there will be no flow of liquid by gravity even when the 
tank is full. When the tank is located so that there will be no 
flow of fuel by gravity, some means must be employed to insure 
the proper passage of fuel from the tank to the carbureter. 
The two methods of doing this in use at the present time are 
the pressure-feed system and the vacuum-feed system. The 
system in which gravity alone is depended on, is known as the 
gravity-feed system. 

77 . Gravity-Feed System.— In systems in which the 
fuel is fed to the carbureter from the tank by gravity, the tank 
is usually located at the top and at the rear of the dashboard, 
or under one of the seats. In some one-seated cars, it is 
directly back of the seat, but in any case it must be high 
enough so that the bottom of the tank is above the highest 
gasoline level in the carbureter, even when the car is ascend¬ 
ing a steep hill, in which case there is a change in the relative 
levels of the tank and carbureter. 

In the gravity-feed system, there must always be a small 
opening in the upper part of the tank, so that air can pass into 
the tank as the fuel flows out. Otherwise, a partial vacuum 
will be formed in the tank, and the flow of fuel will gradually 
decrease until the carbureter does not receive enough to keep 
the engine running. As a general rule, the vent hole is drilled 
in the center of the filler cap. 

78 . Pressure-Feed System.— In the pressure-feed sys¬ 
tem, after the fuel has been poured into the tank, air is pumped 
in by means of a hand-operated pump until a pressure of 1 to 
2 pounds is registered on the gasoline gauge on the dash. 
After the engine begins to run, the pressure is maintained by 
means of an air pump driven by some moving part of the 
engine. This pump is usually provided with a relief valve in 
order to keep the pressure from rising above the desired 
limit. 

The pressure-feed system was in very popular use at one 
time, but has gradually been superseded by the vacuum-feed 
system, which system now forms the regular equipment of the 
large majority of automobiles. 


54 


CARBURETERS 


79. Vacuum-Feed System.— The vacuum-feed fuel 
system consists of means by which fuel from the fuel-supply 
tank is forced by the pressure of the atmosphere into a small 
supplementary tank above the carbureter level and near the 
carbureter, whence the fuel flows to the carbureter by gravity. 

The vacuum-feed fuel system is not applicable to gravity 
fuel tanks in the cowl, but can advantageously be applied to 
gravity fuel tanks under the front seat in order to permit 
raising the carbureter so as to bring it as close to the engine 
cylinders as possible and into a warmer place. Much better 
vaporization of the fuel, and less condensation in the intake 
manifold, is secured by raising the carbureter, and consequently 
the gasoline economy is improved. 

80. Two different models of the Stewart vacuum tank, 
which is the main part of the vacuum-feed fuel system, are 
shown in cross-section in Fig. 28. The operation of both 
models is identical, their only difference being in constructional 
details; the same parts are lettered the same, and hence the 
views of both models can be referred to in reading the 
description. 

The vacuum tank a is cylindrical in form and is divided 
into two chambers. The lower chamber b forms a receptacle 
for gasoline, and is connected by a pipe c to the gasoline inlet 
of the carbureter; this pipe c extends some distance above the 
bottom of the chamber b, and consequently the lower part of b 
serves as a settling chamber for water or other impurities in 
the fuel. By removing a plug d, or opening a drain cock 
screwed in its place, the chamber b can be drained, or a small 
gasoline supply obtained for priming the engine cylinders, etc. 
The lower chamber b at all times is open to the atmosphere by 
way of the passage e and vent pipe /. The upper chamber g, 
while the engine is in operation, is alternately open to the 
atmosphere through the atmospheric valve h, and to the intake 
manifold of the engine by the vacuum valve i ; in the latter case, 
a partial vacuum exists in the upper part of the chamber g. A 
pipe connection j leads from the vacuum valve i to the intake 
manifold, and another pipe connection k leads to the gasoline 


CARBURETERS 


55 


siipply tank; a removable brass-wire gauze strainer l is placed 
at the gasoline inlet to the upper chamber. The lower cham¬ 
ber b and upper chamber g are connected by an elbow m having 



a flap valve n at its lower end. The upper chamber g contains 
the hollow metallic float o, which is connected to the lever p, 
having its fulcrum at q. The lever p is attached by the con¬ 
necting link r to the lever s having its fulcrum at t; lever u, 















































































































56 


CARBURETERS 


which also has its fulcrum at t, has the atmospheric valve h 
and vacuum valve i attached to it. The two levers s and u 
are free to swing on their common fulcrum t independently of 
each other; their free ends are connected together by the 
helical tension spring v, known from its method of attachment 
as an over-center spring, as in operation it moves from one side 
of the center of the fulcrum t to the other. 

81 . The operation of the Stewart vacuum tank is as fol¬ 
lows : With the tank entirely empty, as is the case when the 
device has just been applied to a car or when all fuel has been 
drained from the tank, the float o has fallen to the position 
shown in Fig. 28 (a), where the atmospheric valve h is closed 
and the vacuum valve i is open. If the engine is now cranked, 
either by means of the self-starter or by hand, and the throttle 
is closed, a partial vacuum is created in the intake manifold 
and hence also in the upper chamber g, the flap valve n being 
closed. Consequently, the pressure of the atmosphere on the 
fuel in the main supply tank forces fuel into the upper cham¬ 
ber g through the pipe k. The float o is thereby raised, and also 
the levers p and s, the lever u being at rest, until the continued 
rising of the float brings the over-center spring v to the upper 
side of the fulcrum t, which position is shown in ( b ), when 
this spring suddenly pulls up the lever u, thereby closing the 
vacuum valve i and opening the atmospheric valve h. Air then 
fills the upper part of the upper chamber and gasoline flows by 
gravity past the flap valve n into the lower chamber and to the 
carbureter. The float now falls and as soon as it has fallen 
far enough to bring the over-center spring v to the lower side 
of the fulcrum t, this spring suddenly pulls the lever u down, 
thereby closing the atmospheric valve h and opening the 
vacuum valve i. Fuel now flows from the main supply tank 
into the upper chamber again, raises the float, and finally closes 
the vacuum valve and opens the atmospheric valve again. The 
upper chamber thus alternately partly empties itself into the 
lower chamber and is filled again. 

82 . The vacuum-feed tank is usually placed on the engine 
side of the dashboard; if conditions permit it to be readily 


CARBURETERS 


57 


placed nearer the carbureter, this should be done. The bottom 
of the tank should be at least 3 inches above the fuel level of 
the carbureter, and as much higher as circumstances permit. 
It is absolutely necessary that the top of the vacuum-feed tank 
be above the top of the main fuel supply tank, so that there is 
no danger of gasoline flowing into the vacuum-feed tank by 
gravity when descending steep hills and overflowing through 
the vent pipe /, Fig. 28. The use of a longer vent pipe is 
equivalent to raising the vacuum-feed tank. 

Should the vacuum-feed tank, when empty, refuse to fill 
when the engine is cranked, the probability is that some dirt 
has accumulated on the seat of the flap valve n. A pipe plug 
in the head of the tank, which plug can be seen at w, Fig. 28 ( b ), 
should then be removed and gasoline poured in through a small 
funnel; this gasoline will usually wash all dirt from the seat 
of the flap valve and the tank will operate properly again as 
soon as the pipe plug is replaced. If this treatment fails to 
effect a cure, the tank must be taken apart and the flap valve 
cleaned. It is absolutely necessary that the joint between the 
body and head of the tank be air-tight; a paper gasket 
shellacked on both sides is used to pack the joint. 

If it should be noticed that gasoline is drawn from the tank 
through the pipe j into the intake manifold, which manifests 
itself through the choking and stopping of the engine, it shows 
that the float has sprung a leak and consequently cannot oper¬ 
ate. The remedy is to remove the gasoline from the float and 
then repair it. 



























































